Apparatus and method for wireless communication

ABSTRACT

A wireless communication apparatus which can simultaneously conduct communication on at least two frequency channels is described. The apparatus includes a communication unit which refers to a connection management table to determine a communication system which can be used by a wireless communication terminal using an identifier of the wireless communication terminal, and conducts communication with the wireless communication terminal on a second frequency channel using the communication system, when a request from the wireless communication terminal to change the first frequency channel to the second frequency channel is permitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/686,122, filed Nov. 27, 2012, which is a continuation of U.S.application Ser. No. 12/410,742, filed Mar. 25, 2009, which issued asU.S. Pat. No. 8,345,588 on Jan. 1, 2013, and which is based upon andclaims the benefit of priority from prior Japanese Patent ApplicationNo. 2008-171490, filed Jun. 30, 2008, the entire contents of each ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication apparatuswhich can simultaneously conduct communication through plural frequencychannels and a communication party on the other end which switches amongfrequency channels.

2. Description of the Related Art

Conventionally, in the case where a wireless communication terminalbeing connected to a wireless communication base station, changes afrequency channel while the wireless communication terminal scans to seewhether or not there is a wireless communication base stationconnectable on the new frequency channel, and confirms whether or notthe wireless communication base station whose existence is confirmed bythe scanning is a proper wireless communication base station, wherebythe wireless communication terminal sends a connection request to thewireless communication base station. When the wireless communicationbase station permits the wireless communication terminal to be connectedthereto in response to the connection request, the connection iscompleted, and the wireless communication terminal starts thecommunication with the wireless communication base station.

There are a procedure for moving a wireless communication base stationand wireless communication terminals connected thereto to anotherfrequency channel and a procedure for moving an entire system consistingof only wireless communication terminals to another frequency channel(for example, see IEEE Std.802.11-2007, “IEEE Standard for Informationtechnology—Telecommunications and information exchange betweensystems—Local and metropolitan area networks—Specific requirements; Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)Specifications”, IEEE Computer Society, Jun. 12, 2007). In addition,there are some studies for a system in which communication issimultaneously conducted on plural frequency channels (for example, seeR. Lyenger, et al., “Analysis of Contention-based Multi-channelWireless: MAC for Point-to-multipoint Networks,” Proc. of the 2006International Symposium on a World of Wireless, Mobile and MultimediaNetworks (WoWMoM '06), 26-29 Jun. 2006, 3 pp., Y Huang, et al.,“Architecture and Scheduling Algorithm for a Multi-Channel WirelessInfrastructure Network with Diversity Management Layer,” Proc. of The44th IEEE Conf. on Decision and Control, and the European Control Conf.2005, Dec. 12-15, 2005, pp. 406-410., R. C. Daniels, et al., “Multi-bandModulation, Coding, and Medium Access Control,” doc.: IEEE802.11-07/2780r1, November 2007., JP-A Nos. 2006-246115 (KOKAI),11-205352 (KOKAI), 2004-32210 (KOKAI), and 2002-77965 (KOKAI)).

In IEEE 802.11 wireless LAN, from the viewpoints of coverage securementand effective utilization of frequency channels, there is a discussionthat plural frequency channels are shared under one wirelesscommunication base station (for example, see R. C. Daniels, et al.,“Multi-band Modulation, Coding, and Medium Access Control,” doc.: IEEE802.11-07/2780r1, November 2007.). There are a system in which a controlstation collects pieces of information on wireless communication basestations to allocate an optimum communication channel to wirelesscommunication terminals (for example, see JP-A No. 2006-246115 (KOKAI)and Y. Huang, et al., “Architecture and Scheduling Algorithm for aMulti-Channel Wireless Infrastructure Network with Diversity ManagementLayer,” Proc. of the 44th IEEE Conf. on Decision and Control, and theEuropean Control Conf. 2005, Dec. 12-15, 2005, pp. 406-410.), a systemfor allocating a communication protocol to wireless communicationterminals (for example, see JP-A No. 11-205352 (KOKAI)), a system inwhich a wireless communication base station that can conductcommunication on plural frequency channels newly allocates a frequencychannel to a terminal requesting communication according to wirelesscondition (for example, see JP-A No. 2004-32210 (KOKAI)), and a systemto hand over a connected wireless communication terminal to anothersystem (for example, see JP-A No. 2002-77965 (KOKAI)).

By the conventional techniques, although a wireless communication basestation can perform transmission and reception on plural frequencychannels, wireless communication terminals connected to the wirelesscommunication base station cannot recognize that the wirelesscommunication base station can perform the transmission and reception onthe plural frequency channels. Accordingly, in the case where thewireless communication terminal changes the frequency channel to anotherfrequency channel on which the wireless communication base station canperform the transmission and reception, it is necessary for the wirelesscommunication terminal to scanning again whether or not there is aconnectable wireless communication base station.

Even if plural communication systems such as modulation and codingschemes and security systems can be used by the wireless communicationbase station, in each frequency, the wireless communication base stationdoes not notify the wireless communication terminals of thecommunication systems that are supported in other frequencies.Accordingly, in the case where the wireless communication terminal movesto another frequency channel on which the wireless communication basestation can perform transmission and reception, it is necessary for thewireless communication terminal obtain information on the communicationsystem with which the wireless communication base station is supportedat the frequency channel from the wireless communication base stationagain.

Thus, it is preferable to be able to make a notification that thetransmission and reception can be performed on plural frequencychannels. When plural communication systems such as modulation andcoding schemes and security systems can be used, it is preferable ineach frequency to be able to make a notification of the communicationsystems that are supported in other frequencies. It is preferable that awireless communication apparatus can manage the communication systemswith which another wireless communication apparatus is supported overplural frequency channels.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided awireless communication apparatus which can simultaneously conductcommunication on at least two frequency channels, comprising:notification unit which makes a notification of an identifier of asecond frequency channel and a communication system on a first frequencychannel, the second frequency channel being in a wireless packetreceivable state other than the first frequency channel, thecommunication system being used on the second frequency channel; aconnection management table in which a communication system is retainedalong with an identifier of a wireless communication terminal andidentifiers of frequency channels, the identifiers of the frequencychannels including at least an identifier of the first frequencychannel, the communication system being able to be used by the wirelesscommunication terminal and notified by the wireless communicationterminal when connection of the wireless communication terminal ispermitted on the first frequency channel; and communication unit whichrefers to the connection management table to determine the communicationsystem which can be used by the wireless communication terminal usingthe identifier of the wireless communication terminal, and conductscommunication with the wireless communication terminal on the secondfrequency channel using the communication system, when a request fromthe wireless communication terminal to change the first frequencychannel to the second frequency channel is permitted.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 typically shows the case in which a wireless communication basestation and a wireless communication terminal according to an embodimentare connected to each other;

FIG. 2 is a functional block diagram showing a communication functionunit incorporated into the wireless communication base station andwireless communication terminal of the embodiment;

FIG. 3 is a functional block diagram showing the details of thecommunication function unit in the wireless communication base stationof the embodiment;

FIG. 4 shows an example of an operation on frequencies of a wirelesscommunication base station according to a first embodiment;

FIG. 5 shows another example of the operation on frequencies of thewireless communication base station of the first embodiment;

FIG. 6 shows connection of the wireless communication base station andwireless communication terminal of the first embodiment;

FIG. 7 shows a frame format in a MAC layer of IEEE 802.11 wireless LANof the first embodiment;

FIG. 8 shows contents of a frame control item of FIG. 7 of the firstembodiment;

FIG. 9 shows a state in which the wireless communication base station ofthe first embodiment sends a beacon frame;

FIGS. 10A to 10D show examples of notation of a item in a MAC frame withwhich the wireless communication base station of the first embodimentnotifies the wireless communication terminal of information on anotherfrequency channel;

FIG. 11 shows an example in which two frequency channels partly overlapeach other on the frequency channel in the first embodiment;

FIG. 12 shows another example in which two frequency channels partlyoverlap each other on the frequency channel in the first embodiment;

FIG. 13 shows an example of the notation of the item in the MAC framewhich the wireless communication terminal of the first embodimentnotifies the wireless communication base station of information onanother frequency channel;

FIGS. 14A and 14B show examples of a connection management table in thewireless communication base station of the first embodiment;

FIG. 15 shows an example of the connection management table in thewireless communication terminal of the first embodiment;

FIG. 16 shows a state in which the wireless communication terminal ofthe first embodiment makes a frequency channel change request to thewireless communication base station;

FIG. 17 shows a state in which the wireless communication base stationaccording to a second embodiment sends a beacon frame;

FIG. 18 shows a transmission rate defined by IEEE 802.11a in the secondembodiment;

FIG. 19 shows a relationship between MCS defined by IEEE 802.11n and atransmission rate in a 20-MHz channel bandwidth in the secondembodiment;

FIG. 20 shows an example of a connection management table in thewireless communication base station of the second embodiment;

FIG. 21 shows an example of the connection management table in thewireless communication terminal of the second embodiment;

FIG. 22 shows a beacon frame according to a third embodiment;

FIG. 23 shows an HT capabilities element of the third embodiment;

FIG. 24 shows a capability element of the third embodiment;

FIGS. 25A and 25B show an HT Information element of the thirdembodiment;

FIG. 26 shows an association request frame of the third embodiment;

FIG. 27 shows a state in which a wireless communication base stationaccording to a fourth embodiment sends a beacon frame;

FIG. 28 shows a state in which a wireless communication base stationaccording to a fifth embodiment sends a beacon frame;

FIG. 29 shows a BSS description of the fifth embodiment;

FIG. 30 shows another state in which the wireless communication basestation of the fifth embodiment sends the beacon frame;

FIG. 31 shows a state in which Multi-Channel ID is inserted into framebody fields in a beacon frame and a probe response frame according to asixth embodiment;

FIG. 32 shows a sequence control item according to a seventh embodiment;

FIG. 33 shows an example of a connection management table in a wirelesscommunication base station according to a ninth embodiment;

FIG. 34 shows a state in which a wireless communication base stationaccording to a tenth embodiment sends a beacon frame;

FIG. 35 shows an example of a connection management table in a wirelesscommunication terminal of the tenth embodiment;

FIG. 36 shows an example of the connection management table in awireless communication base station according to an eleventh embodiment;

FIG. 37 shows an example of a connection management table in a wirelesscommunication base station according to a thirteenth embodiment;

FIG. 38 shows an example of the updated connection management table inthe wireless communication base station of the thirteenth embodiment;and

FIG. 39 shows a relationship between a wireless communication basestation and a wireless communication terminal according to a fourteenth.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described in detail below withreference to the drawings.

Referring to FIG. 1, a wireless communication base station (AP (AccessPoint) in the FIG. 101 and a wireless communication terminal (STA(STAtion) in the FIG. 201 are connected to each other. The wirelesscommunication base station 101 may be connected to one or pluralwireless communication terminals other than the wireless communicationterminal 201, or may be connected to another one or plural wirelesscommunication base stations, or may be connected to a wired network. Thewireless communication terminal 201 may be connected to another one orplural wireless communication terminals connected to the wirelesscommunication base station 101. As used herein, “connection” between thewireless communication base station and the wireless communicationterminal, between the wireless communication base stations, or betweenthe wireless communication terminals shall mean a state in which thewireless communication terminals mutually recognize the existence andhas exchanged notifications of capabilities necessary for thecommunication. The wireless communication can be conducted between thewireless communication base station and wireless communication terminalthat are in the connected state, between the wireless communication basestations in the connected state, or between the wireless communicationterminals in the connected state. The wireless communication basestation and the wireless communication terminal(s) connected to thewireless communication base station correspond to a component called aninfrastructure BSS (Basic Service Set) in the IEEE 802.11 wireless LANsystem. Sometimes the infrastructure BSS is simply referred to as BSS.

FIG. 2 is a functional block diagram showing a communication functionunit incorporated in the wireless communication base station andwireless communication terminal of the embodiment. Referring to FIG. 2,a wireless communication function unit 8 includes a baseband processingunit 12, a frequency conversion circuit 6, and a wireless antenna 10.The wireless communication function unit 8 generates data whosecommunication is conducted through a Logical Link Control (LLC) layerdefined by, for example, an IEEE 802 standard. The wirelesscommunication function unit 8 may be connected to a user interface thatdisplays the data on a display. In the configuration of FIG. 1, thewireless communication base station is connected to the wired network,and the wireless communication function unit 8 of the wirelesscommunication base station can exchange the data with other wirelesscommunication base stations or terminals including wirelesscommunication terminals that are located on the wired network.

The baseband processing unit 12 includes a MAC (Media Access Control)unit 2 and a PHY (PHYsical) unit 4. The baseband processing unit 12 ispursuant to an IEEE 802.11 wireless LAN (including series of amendmentand supplement standards such as 802.11a, 802.11b, 802.11e, 802.11g,802.11h, 802.11i, 802.11j, and 802.11n after IEEE 802.11, the same holdstrue for the following descriptions) system. The MAC unit 2 performs aspecified operation relating to a MAC layer, and the PHY unit 4 performsa specified operation relating to a PHY layer. The MAC unit 2 includes amemory for a work area and a frame buffer. The MAC unit 2 performs MACheader processing, access control for transmitting a MAC frame,reception frame processing including response frame transmission andmanagement relating to a set up between wireless communicationterminals. The latter-mentioned wireless communication terminalinformation or wireless communication base station information is alsostored in the memory. Instead of being incorporated into the MAC unit 2in order to specialize in the MAC processing, the memory may be providedoutside the MAC unit 2, and may be also used in other pieces ofprocessing than the MAC layer. The PHY unit 4 is connected to the MACunit 2, and performs PLCP (Physical Layer Convergence Protocol) headerprocessing, modulation and demodulation processing, and A/D conversionprocessing.

The frequency conversion circuit 6 is connected to the PHY unit 4. Thefrequency conversion circuit 6 converts a frequency of a transmissionsignal in a stepwise manner in order to radiate a radio wave from anantenna 10, and converts a frequency of a reception signal in a stepwisemanner such that the received radio wave can be processed by the PHYunit 4.

For example, the data fed from the LLC layer is converted into the MACframe by the MAC unit 2, and the MAC frame is converted into the PHYpacket by the PHY unit 4 and is sent as a radio signal from the antenna10 through the frequency conversion circuit 6. On the contrary, theradio signal received from the antenna 10 is processed through thefrequency conversion circuit 6, PHY unit 4, and MAC unit 2, and the dataaddressed to the terminal is supplied to a higher layer such as the LLClayer.

FIG. 3 shows a detailed functional block diagram of the wirelesscommunication base station of the embodiment. The reference numerals ofFIG. 3 are in common with those of FIG. 2. In the wireless communicationbase station, at least two access control units (access control unit forPHY1 31 and access control unit for PHY2 32 in FIG. 3) corresponding tothe PHY unit 4 are provided in the MAC unit 2, the PHY unit 4 includesat least two processing units (PHY1 processing unit 33 and PHY2processing unit 34 in FIG. 3) corresponding to the PHY layer, the accesscontrol units are respectively connected to the PHY processing units (inFIG. 3, the access control unit for PHY1 31 is connected to the PHY1processing unit 33, and the access control unit for PHY2 32 is connectedto the PHY2 processing unit 34), the PHY processing units arerespectively connected to the frequency conversion circuits (firstfrequency conversion circuit 35 and second frequency conversion circuit36 of FIG. 3), and the frequency conversion circuits are respectivelyconnected to antennas. The access control units for PHY (access controlunit for PHY1 31 and access control unit for PHY2 32 of FIG. 3) in theMAC unit 2 are connected to a MAC layer management unit (correspondingto a portion that performs MAC sub-Layer Management Entity (MLME) inIEEE 802.11 wireless LAN) 30, and the access control units for PHY areconnected to each other (arrow between the access control unit for PHY131 and access control unit for PHY2 32 of FIG. 3). For the frequencyconversion circuit 8 and the antenna 10, a configuration other than theconfiguration of FIG. 3 may be adopted when the radio signals havingdifferent frequencies can simultaneously be transmitted or received fromthe antenna 10.

For example, the radio signal sent through the access control unit forPHY1 31, PHY1 processing unit 33, and first frequency conversion circuit35 of FIG. 3 is one that is supported with IEEE 802.11b or IEEE 802.11gwhich is a 2.4 GHz bandwidth wireless LAN or IEEE 802.11n operated in a2.4 GHz bandwidth. For example, the radio signal sent through the accesscontrol unit for PHY2 32, PHY2 processing unit 34, and second frequencyconversion circuit 36 is one that is supported with IEEE 802.11a whichis a 5 GHz bandwidth wireless LAN or IEEE 802.11n operated in a 5 GHzbandwidth.

In this case, the access control unit for PHY1 31 performs control totransmit the radio signal using access control parameters (a slotlength, a SIFS (Short Inter-Frame Space) length, and the like that areused to perform CSMA/CA) and information on the modulation and codingscheme according to IEEE 802.11b, IEEE 802.11g, or 2.4 GHz bandwidthIEEE 802.11n. The access control unit for PHY2 32 performs control totransmit the radio signal using the access control parameters and theinformation on the modulation and coding scheme according to IEEE802.11a or 5 GHz bandwidth IEEE 802.11n. Thus, in the wirelesscommunication base station, the communication using differentextensions/amendments in the same standard may be conductedsimultaneously. The communication may be conducted by not only thedifferent extensions/amendments in the same standard, such as 2.4 GHzbandwidth IEEE 802.11g and 5 GHz bandwidth IEEE 802.11a asabove-described example, but different frequency channels used in thesame extension/amendment of the same standard, like channel numbers 36and 44 of frequency channels used in 5 GHz bandwidth IEEE 802.11a.

Alternatively, for example, the radio signal sent through the accesscontrol unit for PHY1 31, PHY1 processing unit 33, and first frequencyconversion circuit 35 of FIG. 3 is a 5 GHz-band signal and the radiosignal sent through the access control unit for PHY2 32, the PHY2processing unit 34, and the second frequency conversion circuit 36 is a60 GHz bandwidth (so-called millimeter wave bandwidth of 57 GHz to 62GHz) signal. Here, the access control unit for PHY1 31 performs controlusing parameters and information relating to transmission of the 5GHz-band radio signal, and the access control unit for PHY2 32 performscontrol using parameters and information relating to transmission of theradio signal in the 60 GHz bandwidth (for example, frequency bandwidthof 57 GHz to 66 GHz). A wireless communication base station may be suchas this using communication systems having largely different frequencybandwidths simultaneously.

Alternatively, for example, the radio signal sent through the accesscontrol unit for PHY1 31, PHY1 processing unit 33, and first frequencyconversion circuit 35 of FIG. 3 is for a GSM or 3GPP portable telephone(cellular phone) and the radio signal sent through the access controlunit for PHY2 32, PHY2 processing unit 34, and second frequencyconversion circuit 36 is for a wireless LAN. Here, the access controlunit for PHY1 31 performs control using parameters and informationrelating to transmission of the radio signal for the GSM or 3GPPportable telephone (cellular phone), and the access control unit forPHY2 32 performs control using parameters and information relating totransmission of the radio signal for the wireless LAN. Or, thecommunication system may be those of an 802.16 system (WiMAX system) ofa Wireless Metropolitan Area Network (WMAN) or an 802.15 system (WiMediasystem) of a Wireless Personal Area Network (WPAN). A wirelesscommunication base station may be such as this using communicationsystems for different wireless communication standards simultaneously.

First Embodiment

FIG. 4 shows an example of an operation on frequencies of a wirelesscommunication base station according to a first embodiment.

The wireless communication base station (designated by AP (Access Point)in FIG. 4,) can simultaneously conduct communication on plural frequencychannels. Although an example of two different frequency channels isshown in FIG. 4, the communication can simultaneously be conducted onthree or more different frequency channels as shown in FIG. 5.

Each frequency channel is defined, for example, by a set of a centerfrequency (designated by f1 and f2 in FIG. 4) and a channel bandwidth(designated by BW1 and BW2 in FIG. 4), and a channel identifier(designated by ch.1 and ch.2 in FIG. 4) used to distinguish thefrequency channels from one another. Accordingly, in FIG. 4, the channelidentifier ch.1 has the center frequency f1 and the channel bandwidthBW1.

On the other hand, each frequency channel belongs to a large frequencybandwidth. When the frequency channel is classified by the frequencybandwidth, the reorganization of the frequency bandwidth may be enough.For example, the frequency channels may be indicated by levels of theidentifier ch.1 meaning the 5 GHz bandwidth and the identifier ch.2meaning the 60 GHz bandwidth. This is because basically there is nodifference in operation at the detailed frequency channel level in thefrequency bandwidth (although there may be regulatory limitations inchanging such as transmission power or access parameters). In the casewhere the wireless communication terminal (including wirelesscommunication base station) is operated pursuant to IEEE 802.11b, IEEE802.11g, or IEEE 802.11n in the 2.4 GHz bandwidth, a basic function withwhich the wireless communication terminal is supported is independent ofthe detailed frequency channel in the 2.4 GHz bandwidth. The same holdstrue for the case in which the wireless communication terminal isoperated pursuant to IEEE 802.11a or IEEE 802.11n in the 5 GHzbandwidth, and the same holds true for the 60 GHz bandwidth.

As used herein, “communication can simultaneously be conducted on pluralfrequency channels” shall mean that, assuming that two channels ch.1 andch.2 exist, when the wireless communication terminals transmit the radiosignals on each of the two channels, ch.1 and ch.2, to the wirelesscommunication base station, the wireless communication base stationdemodulates and decodes the radio signals based on the configuration ofFIG. 3 and transfers the radio signals to the MAC unit 2, and the MACunit 2 performs proper reception processing on the radio signal as a MACframe.

The meaning of “communication can simultaneously be conducted on pluralfrequency channels” will specifically be described with reference toFIG. 6. In FIG. 6, the wireless communication terminal 201 transmits theradio signal on the channel ch.1 to the wireless communication basestation 101, and the wireless communication terminal 202 transmits theradio signal on the channel ch.2 to the wireless communication basestation 101. Even if the radio signals are transmitted at the same timeor in a partially overlapping time, in the wireless communication basestation 101, the MAC unit 2 can perform the proper reception processingon the radio signals as MAC frames through the demodulation anddecoding.

For example, the wireless communication base station 101 and thewireless communication terminal 201 are pursuant to IEEE 802.11g in thechannel ch.1, and the wireless communication terminal 201 sends a proberequest frame to the wireless communication base station 101 in order tolearn parameters used by the wireless communication base station 101 informing the infrastructure BSS on the channel ch.1. The wirelesscommunication base station 101 sends back an ack frame in response tothe reception of the probe request frame and generates a probe responseframe indicating parameters used in the infrastructure BSS, and sendsthe probe response frame to the wireless communication terminal 201. Onthe other hand, the wireless communication base station 101 and thewireless communication terminal 202 are pursuant to IEEE 802.11a in thechannel ch.2, the wireless communication terminal 202 subscribes to theinfrastructure BSS formed on the channel ch.2 by the wirelesscommunication base station 101, and sends an authentication frame to thewireless communication base station 101 in order to establish connectionwith the wireless communication base station 101 to start data exchange(that is, communication). Then, the wireless communication base station101 sends back the ack frame in response to the reception of theauthentication frame, and sends the authentication frame in response tocontents of the authentication frame from the wireless communicationterminal 202. Through the authentication processing, a set up such as touse WEP (Wired Equivalent Privacy), which is an encryption system, canbe established. When a series of pieces of processing relating to theauthentication is completed between the wireless communication terminal202 and the wireless communication base station 101, the wirelesscommunication terminal 202 sends an association request frame to thewireless communication base station 101 in order to notify the wirelesscommunication base station 101 of its capability, and to be able tostart the actual data exchange in the infrastructure BSS. After sendingback the ack frame in response to the reception of the associationrequest frame, the wireless communication base station 101 sends anassociation response frame to the wireless communication terminal 202.The association response frame includes the capability possessed by thewireless communication base station 101 and a response as to whether ornot an association request is accepted. After the series of frameexchanges for connection set up, the wireless communication terminal 202starts exchanging data frames with the wireless communication basestation 101.

Thus, the wireless communication base station 101 can independentlyperform transmission and reception on the channels ch.1 and ch.2. On theother hand, the wireless communication terminal 201 can conduct thecommunication pursuant to IEEE 802.11g on the channel ch.1 and canconduct the communication pursuant to IEEE 802.11a on the channel ch.2.The wireless communication terminal 201 includes at least one frequencyconversion circuit shown in FIG. 2, and can perform transmission andreception at least on either the channel ch.1 or ch.2 when actuallytransmitting the radio signal. Alternatively, the wireless communicationterminal 201 may have the configuration shown in FIG. 3 like thewireless communication base station 101, and may simultaneously conductthe communication on channels ch.1 and ch.2.

Here, using the channel ch.1, the wireless communication base station101 notifies the wireless communication terminal 201 of the informationabout the frequency channel ch.2. The notification may be annunciation.The annunciation shall mean that a large indefinite number of wirelesscommunication terminals (including surrounding wireless communicationbase stations) are notified. For example, in the IEEE 802.11 wirelessLAN standard, the annunciation may be performed using a frame having abroadcast address such as a beacon frame.

A frame format of the MAC layer in the IEEE 802.11 wireless LAN will bedescribed with reference to FIG. 7.

Referring to FIG. 7, a MAC header portion ranges from a frame controlitem up to the point where the frame body item follows (i.e., to anaddress 4 in FIG. 7.) The MAC header portion may also include a QoScontrol item which is used in performing QoS control.

FIG. 8 shows contents of the frame control item of FIG. 7. A bitposition of each item is designated by (X=1, 2, . . . ).

In a IEEE 802.11 wireless LAN system, as types of transmitting MACframes, there are a data frame for transmitting data generated by alayer above the MAC layer (however, sometimes empty data is generated bythe MAC layer and transmitted), a management frame for transmittingmanagement information on a MAC layer level, and a control framerelating to access control in the MAC layer. These classifications areindicated by a type item of the frame control item. For example thebeacon frame belongs to the management frame, and {B2,B3}={0,0}indicating the management frame is described in the type item. The typeitem will be {B2,B3}={0,1} for the data frame, and {B2,B3}={1,0} for thecontrol frame. On the contrary, it can be said that the data frame, themanagement frame, and the control frame can be distinguished from oneanother by the description of the type item. In addition to the largeclassification of the type of the frame, a subtype item indicates adetailed type of the frame within the large classification. For example,in the beacon frame, the subtype item. is {B4,B5,B6,B7}={0,0,0,1}.

FIG. 7 shows the most versatile configuration, and some of the item areomitted in some frames. For example, there are four address fields inFIG. 7. All the address fields are used in the case where the data frameis sent between the wireless communication base stations. Basically, anaddress 1, an address 2, and an address 3 are used in the case of otherdata frames, the address 1, the address 2, and the address 3 are used inthe case of management frames, only the address 1 or the address 1 andthe address 2 are used in the case of control frames (however, there aresome exceptions in the case where a control frame is contained in theother control frame).

In IEEE 802.11, all the bits of the address 1 item are set to 1 in abroadcast frame. The address 1 item indicates a direct transmissionaddress. A broadcast frame is sent to all the wireless communicationterminals without specifying the transmission address. Additionally,there is a multicast frame as a frame sent to plural wirelesscommunication terminals. In a multicast frame, an initial bit (specifiedas an individual/group bit) of an initial octet item of the address 1item is set to 1 (that is, group bit), and each of the particular valuesare specified to address a particular group of wireless communicationterminal. A broadcast frame is a special case of a multicast frame. Anda frame sent to a single wireless communication terminal is called aunicast frame, in contrast with a group address frame set to pluralwireless communication terminals. When a wireless communication terminalreceives a broadcast frame in which all the bits of the address 1 itemare set to 1, or when a wireless communication terminal receives amulticast frame in which the multicast address indicated in the address1 item includes the address of the terminal itself, the wirelesscommunication terminal recognizes that the broadcast frame or themulticast frame is addressed to the terminal itself, and performsreception processing. According to some of the type of a frame, thewireless communication terminal performs the reception processing afterconfirming whether the address item (if the frame is a data frame andtransmitted from the wireless communication base station to the wirelesscommunication terminal, then it will be the address 2 item and if theframe is a management frame, then it will be the item address 3 item) inwhich BSSID for identifying the BSS is described, shows the BSSID of BSSto which the wireless communication terminal belongs.

In a management frame, information produced in the MAC layer is insertedin the frame body item. In a data frame, data generated by the layerabove the MAC and transferred to the MAC layer is inserted in the framebody item. In a control frame, sometimes information produced by the MAClayer is inserted in the frame body item, and sometimes the frame bodyitem does not exist.

The operation in which the wireless communication base station 101broadcasts the information about the frequency channel ch.2 on thechannel ch.1 will be described with reference to an example in which abeacon frame of IEEE 802.11 is used. Basic information relating to theBSS including synchronous information is inserted in the beacon frame.As shown in FIG. 9, when the wireless communication base station 101sends the beacon frame on the channel ch.1, information about thefrequency channel ch.2 is also inserted in the beacon frame. Here, theinformation about the frequency channel ch.2 is the channel identifierch.2 and a communication system used on the channel ch.2. In FIG. 9, itis shown that the wireless communication base station 101 is supportedwith IEEE 802.11a and IEEE 802.11n by the information on thecommunication system for the channel ch.2 as an example. In the firstembodiment, a communication standard system is inserted as theinformation on the communication system. As described above, IEEE802.11a and IEEE 802.11n are extended standards in the communicationstandard system of IEEE 802.11 and the description may be in such level,or may be in a larger category such as IEEE 802.11 and GSM. For example,as a communication standard system for 60 GHz bandwidth, there is onedefined by IEEE 802.15 (802.15.3c), but one defined by IEEE 802.11 canbe also expected. In such case when the wireless communication basestation 101 is supported with the millimeter wave defined by IEEE 802.11in the channel ch.2 the extended system of the IEEE 802.11 standardcorresponding to the millimeter wave bandwidth is notified. In the caseof IEEE 802.15.3c, a notification of IEEE 802.15.3c is made as thecommunication standard system. In IEEE 802.15.3c, plural systems existin the PHY layer. When the wireless communication on base station 101 issupported with a part of the plural systems, a notification is made upto the level where the supported systems can be identified.

When the specific communication systems in the channels ch.1 and ch.2can be distinguished from each other by the frequency bandwidths towhich the frequency channels of the channels ch.1 and ch.2 belong, thespecific communication system can be omitted by putting the channelidentifiers ch.1 and ch.2. In this case, the notification of thecommunication system is made by inserting the channel identifier.Assuming that IEEE 802.11 wireless LAN is used, when the channel ch.1 isin the 5 GHz bandwidth, it implies the support of IEEE 802.11a/nbandwidth, and when the channel ch.2 is in the 60 GHz bandwidth itimplies the support of the millimeter wave standard defined by IEEE802.11. When the notification or a connection request is made in theframe format defined by IEEE 802.11, it will also show that thecommunication is conducted based on the IEEE 802.11 wireless LANstandard.

Alternatively, the frequency channel information on the channel ch.1 orch.2 can be shown in the form of a frequency bandwidth level and asubset of frequency channels allocated in the frequency bandwidth. Inthe case where the wireless communication base station 101 correspondsto some of the subsets of the plural frequency channels in the frequencybandwidth, one may define those subsets and by indicating the frequencybandwidth and the names of the subsets, and it is possible for thewireless communication base station 101 to show its support to groups offrequency channels in the frequency bandwidth. Therefore, for example,notifications such as ch.1=2.4 GHz bandwidth channel subset 1(corresponding only to channel number 1) and ch.2=5 GHz bandwidthchannel subset 10 (corresponding to channel numbers 36, 40, and 52) canbe made.

FIG. 9 shows an example in which a notification of the position of thefrequency channel is made with the channel identifier ch.2. When forexample the channel bandwidths of the frequency channels used by thecommunication base station 101 are allocated at regular intervals, thecenter frequency and the channel bandwidth can be specified by thechannel identifier. Even in an irregular arrangement of the frequencychannels, when information on the arrangement of the frequency channelsis previously shared between the wireless communication base station andthe wireless communication terminal, the wireless communication terminalcan learn the center frequency (f2 in the example) and channel bandwidth(BW2 in the example) of the frequency channel (frequency channel havingthe channel identifier ch.2 in the example) from the channel identifiernotified by the wireless communication base station. Therefore, asubfield such as FIG. 10A may be provided in the frame body item of thebeacon frame to indicate the information on other frequency channelsused by the wireless communication base station 101.

On the other hand, sometimes there is a case where the wirelesscommunication terminal cannot specify the necessary frequency channelinformation such as the center frequency and the channel bandwidth onlyby the channel identifier.

IEEE 802.11a uses the channel bandwidth of 20 MHz, and IEEE 802.11n hasthe channel bandwidth of 40 MHz as an option in addition to the channelbandwidth of 20 MHz. In the case where different channel bandwidths canbe used such that the channel bandwidth BW1 of the channel ch.1 is 20MHz while the channel bandwidth BW2 of the channel ch.2 is 40 MHz,information on the channel bandwidth BW2 is added as the informationabout the frequency channel ch.2. The actual channel bandwidth (forexample, 40 MHz) can be described as the information on the channelbandwidth BW2, or the information on the channel bandwidth can benormalized by the reference channel bandwidth and expressed by aninteger when different channel bandwidths are an integral multiple oftwo or more of the reference channel bandwidth (for example, 20 MHz). Inthe example, the channel bandwidth BW2 is double the channel bandwidthBW1, so that the channel bandwidth BW2 can be expressed by two. When thereference channel bandwidth used in the normalization is known by thewireless communication terminal, a normalized value is directly insertedas the channel bandwidth information. In the case where the referencechannel bandwidth is not known, assuming that the channel used as thereference is the current frequency channel (ch.1, in the example) onwhich the notification of the information on another frequency channelis made, and by the information about the current frequency channelitself (in the example, the channel bandwidth BW1 as the information onthe channel ch.1) been announced, the wireless communication terminalcan specify the information on another frequency channel. In the IEEE802.11 wireless LAN standard when the bandwidth is extended in theregulatory class, a frequency direction can be expressed by defining aregulatory class in addition to the information (such as the centerfrequency position and the channel bandwidth) on the reference frequencychannel A new supported channel bandwidth (for example, 60 MHz or 80MHz) and the extended frequency direction may be defined if necessary,and in the regulatory class such regulatory class can be used in pairwith the channel identifier to express the new supported channel widthand its extended frequency direction.

Sometimes there may be a case where the center frequency cannot bespecified only by the channel identifier because, for example, thecenter frequency channels are not allocated at regular intervals. Insuch case, the information of the center frequency f2 is added as theinformation about the frequency channel ch.2. Obviously the notificationcan be made by a set of the information on the center frequency and theinformation on the channel bandwidth along with the channel identifier.FIG. 10B shows an example of the subfield inserted in the frame bodyitem of the frame when the notification of the center frequency andchannel bandwidth is made along with the channel identifier as theinformation on another frequency channel (ch.2, in the example) used bythe wireless communication base station 101.

Two or more frequency channels may partially overlap on the frequency.For example, in the case where a channel with the double channelbandwidth spreads in the increasing direction of the frequency withrespect to the frequency channel of the channel ch.1 as shown in FIG.11, when the center frequency f1 and the channel bandwidth BW1 is knownby the wireless communication terminal as the information on the channelch.1 due to the beacon frame transmitted on the channel ch.1, and whenthe information in the channel ch.2 indicates that the channel bandwidthfurther occupies another amount of the channel bandwidth BW1 in theincreasing direction of the frequency based on the center frequency f1and the channel bandwidth BW1 (in the example, “+2”), the wirelesscommunication terminal 201 can specify the information about thefrequency channel ch.2. Here, the subfield inserted in the frame bodyitem of the frame may be as FIG. 10C. Based on this example of FIG. 10C,in the case where the double channel bandwidth is widened in thedecreasing direction of the frequency as shown in FIG. 12, “−2” isdescribed as the information about the frequency channel ch.2 while thenotification of the information on the channel ch.1 is made. When thecenter frequency f1 and channel bandwidth BW1 is unknown to the wirelesscommunication terminal as the information on the channel ch.1, suchinformation can be announced together using the beacon frame on thechannel ch.1. When the extended channel bandwidth is an optional featureas the 40 MHz in IEEE 802.11n and the wireless communication terminaldoes not always need to support the operation on the channel ch.2, itcan be notified by a subfield in which a mandatory/option is describedas information on another frequency channel as shown in FIG. 10D, and aflag of “1” set in the subfield to show it is optional. Also in thiscase, a supported channel bandwidth (such as 60 MHz or 80 MHz) andextended direction in frequency may be defined as the regulatory classand expressed by the regulatory class and the reference frequencychannel on request.

The series of expressions of the pieces of channel information andcommunication systems can be also applied to the case for a wirelesscommunication terminal described later.

When the information on another frequency channel (in the example, ch.2)is announced by a beacon frame of the channel ch.1, the wirelesscommunication terminal 201 can recognize that the communication can beconducted on another frequency channel (in the example, ch.2) with thewireless communication base station 101 which transmits the beaconframe, and which communication system is used on another frequencychannel ch.2.

In FIG. 9, when the wireless communication terminal 201 recognizes thatthe wireless communication base station 101 uses IEEE 802.11g on thechannel ch.1 while using IEEE 802.11a on the channel ch.2, in order forthe wireless communication terminal 201 to start communication with thewireless communication base station 101 on the channel ch.1 which is thefrequency channel currently being received, the wireless communicationterminal 201 starts a procedure for setting up a connection with thewireless communication base station 101. The procedure in which thewireless communication terminal 201 finds the wireless communicationbase station 101 and sets up a connection with the wirelesscommunication base station 101 will be described referring to theprocedure in IEEE 802.11. The wireless communication terminal 201searches (scans) for the wireless communication base station to connecton its transmittable and receivable frequency channel. In a scanningoperation, there are a passive scanning mode and an active scanningmode. In passive scanning, the wireless communication terminal finds thewireless communication base station by receiving a beacon frame sent onthe frequency channel from the wireless communication base station. Inactive scanning, a probe request frame is sent, and when a proberesponse frame is received in response to the probe request frame by theprobe response frame, the wireless communication terminal can find thewireless communication base station. The probe request frame may be sentwithout specifying the destination address (address 1 item in FIG. 7 formanagement frames), i.e., sent as a broadcast frame, or may be sent to aparticular wireless communication base station in a unicast format. Whenreceiving the probe request frame from the wireless communicationterminal 201, the wireless communication base station 101 first respondsby an ack frame if the probe request frame was a unicast frame, andgenerates a probe response frame, to send to the wireless communicationterminal 201. The same information on another frequency channel asinserted in the beacon frame is inserted in the frame body item of theprobe response frame. Alternatively, even if the information on anotherfrequency channel is not inserted in the beacon frame by the wirelesscommunication base station 101, in the case where the wirelesscommunication terminal 201 makes a request of the information on anotherfrequency channel by the probe request frame, the information on anotherfrequency channel may be inserted in the probe response frame by thewireless communication base station 101. After the scanning operation,the wireless communication terminal 201 performs authenticationprocedures and association procedures. In the first embodiment, whentransmitting an association request frame to the wireless communicationbase station 101, the wireless communication terminal 201 notifies thewireless communication base station 101 of the communication systemwhich can be used in the channel ch.2 in the subfield indicating itscapability within the frame body item. For example, the wirelesscommunication terminal 201 notifies the wireless communication basestation 101 that the communication can be conducted pursuant to IEEE802.11a on the channel ch.2 with the subfield having the format of FIG.13 provided in an association request frame. Obviously, in addition tothe format of FIG. 13, a format similar to the ones shown in FIG. 10 A-Dthe wireless communication base station 101 informs the supportedfrequency channel and communication system in the beacon frames and inthe probe response frames can be used.

The wireless communication base station 101 receives the associationrequest frame from the wireless communication terminal 201 on thechannel ch.1 using IEEE 802.11g, and the corresponding capability of thewireless communication terminal 201 to conduct communication using IEEE802.11g on the channel ch.1 is described in the association requestframe. In addition, the wireless communication base station 101 canrecognize that communication with the wireless communication terminal201 can be conducted using IEEE 802.11a on the channel ch.2. Currentlythe frequency channel ch.1 is used to conduct communication withwireless communication terminal 201.

Now it is considered that another wireless communication terminal 202notifies the wireless communication base station 101 of the frequencychannel and communication system which can be used by the wirelesscommunication terminal 202 using the association request frame. Forexample, the wireless communication terminal 202 notifies the wirelesscommunication base station 101 that the communication can be conductedpursuant to IEEE 802.11a/g/n. It is assumed that the frequency channelch.2 is currently used in the communication between the wirelesscommunication terminal 202 and the wireless communication base station101.

Then, the wireless communication base station 101 generates a connectionmanagement table therein as shown in FIG. 14A, where the connectionmanagement table holds the information on the communication capabilitiesof the wireless communication terminal. The connection management tablemay be retained in the MAC layer management unit 30 of FIG. 3, or may beretained in an external memory connected to the MAC layer managementunit 30. The wireless communication base station 101 may notify thewireless communication terminals that the wireless communication basestation 101 has a capability to retain information on wirelesscommunication terminals between the frequency channels which it supportsin beacon and probe response frames. In FIG. 14A, the terminalidentifier of the wireless communication terminal 201 (STA201) isdescribed in the item “terminal identifier”, the frequency channelidentifies of the supported frequency channels notified by the wirelesscommunication terminal 201 to the wireless communication base station101 is described in the item “supportable channel”, the communicationsystem which can be supported in each of the frequency channels isdescribed in the item “supported communication system”, and theidentifier of the frequency channel on which the communication iscurrently conducted is described in the item “channel used”. Here, thewireless communication terminal 201 notifies the wireless communicationbase station 101 by the association request frame that the wirelesscommunication terminal 201 supported the frequency channel ch.2 and theIEEE 802.11a is the communication system which can be used on thefrequency channel ch.2. Therefore, the wireless communication basestation 101 can enter the information regarding the frequency channelch.2 in the connection management table. On the other hands, as theassociation request frame is sent on the frequency channel ch.1, and theinformation for conducting the communication on the current channel,that is, the frequency channel ch.1 is also given to use IEEE 802.11g inthe association request frame, the information on the frequency channelch.1 can be compensated and retained as the information in theconnection management table even if the support of the frequency channelch.1 is not explicitly described in the association request frame.

It is not always necessary for the wireless communication terminalidentifier to be the actual MAC address of the wireless communicationterminal, and the description can be in other ways if the wirelesscommunication base station can uniquely identify each of the wirelesscommunication terminals. For example, in IEEE 802.11, an associationidentifier (AID) is inserted in the frame body item of the associationresponse frame which is sent in response to the association requestframe from the wireless communication terminal (for example, 201) by thewireless communication base station 101. An AID is a unique value of 1to 2007 which is allocated to each wireless communication terminalduring the association process and used to identify the wirelesscommunication terminals by the wireless communication base station. Inthe case where an AID is inserted in an AID item of a frame consistingof two octets, “1”s are inserted in bit 14 and bit 15, and the uniquevalue (AID) of 1 to 2007 is inserted in the remaining bits, a bit 0 to abit 13. When the wireless communication base station 101 receives theassociation request frame from the wireless communication terminal 201,an STA management entity (SME) makes a determination of the connectionwith the wireless communication terminal 201 through the MAC layermanagement unit 30 of FIG. 3, and the wireless communication basestation 101 notifies the wireless communication terminal 201 of theconnection permission by a status code subfield of the associationresponse frame (status code subfield is also used in the case of thenotification of the connection rejection). Here, the MAC layermanagement unit 30 records the AID allocated to the wirelesscommunication terminal 201 in the item for the wireless terminalidentifier in the connection management table, extracts the pieces ofinformation about the frequency channel and communication system whichthe wireless communication terminal 201 supported from the associationrequest frame, and writes the pieces of information about the frequencychannel and communication system in a predetermined item correspondingto the wireless communication terminal identifier. Although not shown inFIGS. 2 and 3, an SME is connected to the MAC layer management unit 30(included in the MAC unit 2 in FIG. 2), and determines an operationpolicy (including other layers) of the wireless communication terminalor the wireless communication base station.

When a single baseline communication standard is used across pluralfrequency channels in the wireless communication base station but whenthe frequency channels differ from one another in the supported extendedlevel from the base line, interoperability between the extendedstandards can be expected. For example, the backward compatibility withIEEE 802.11b is required in IEEE 802.11g, the backward compatibilitywith IEEE 802.11a is required in the 5 GHz bandwidth in IEEE 802.11n,and the backward compatibility with IEEE 802.11b/g is required in the2.4 GHz bandwidth in IEEE 802.11n. One can understand that thecompatibility with IEEE 802.11b is also obtained by the notification ofthe compatibility with IEEE 802.11g. One can understand that thecompatibility with IEEE 802.11a is also obtained by the notifications ofthe compatibility with IEEE 802.11n and the support of the frequencychannel ch.2 in the 5 GHz bandwidth. When the frequency channelsupported with the extended standard can be specified while the backwardcompatibility is obtained between the extended standards, theinformation on the comprehensive standard or supported frequency channelmay be omitted and the connection management information may be retainedas FIG. 14B.

On the other hand, the wireless communication terminal 201 recognizesthat the wireless communication base station 101 can also conduct thecommunication on the frequency channel ch.2 and that the wirelesscommunication base station 101 is supported with the communicationsystem of IEEE 802.11a on the frequency channel ch.2 (because thewireless communication terminal 201 is not supported with IEEE 802.11n,the wireless communication terminal 201 does not need to recognize thatthe wireless communication base station 101 is supported with IEEE802.11n) by the beacon frame or the probe response frame received fromthe wireless communication base station 101, so that the wirelesscommunication terminal 201 can generate at least a connection managementtable as FIG. 15 when receiving the notification of the connectionpermission by the association response frame. When the wirelesscommunication base station to connect is uniquely determined, the basestation identifier in FIG. 15 may be omitted (after the identifier ofthe wireless communication base station to connect while is retained inanother information management place, for example, a ManagementInformation Base (MIB) as a MIB value) and can be referred to. In FIG.15, the communication system 802.11n which the wireless communicationterminal 201 does not supported is not recorded as in the communicationsystem on the frequency channel ch.2 even if it is described in thebeacon frame or the probe response frame because the wirelesscommunication terminal 201 does not supported it. However, in the casewhere the wireless communication terminal 201 can recognize thecommunication system 802.11n although not supported with, thecommunication system 802.11n may be described in the item of thecommunication system corresponding to the frequency channel ch.2. Thewireless communication terminal 201 may generate the connectionmanagement table as FIG. 15 before receiving the connection permissionby the association response frame, and may recognize the current statuswhether or not the connection permission is received by writing in the“channel used” column when receiving the connection permission. By doingthis, the wireless communication terminal 201 can collect pieces ofinformation on candidate plural wireless communication base stations andthe frequency channels and communication system which the wirelesscommunication base stations is support, and select a wirelesscommunication base station suitable for the communication request of thewireless communication terminal 201 as the one to connect, and initiatethe connection set up with the selected wireless communication basestation.

When receiving the association response frame from the wirelesscommunication base station 101, the wireless communication terminal 201can start the communication on the frequency channel ch.1, and alsorecognize that the wireless communication base station 101 can conductthe communication on the frequency channel ch.2 using IEEE 802.11a fromthe connection management table of FIG. 15. Therefore, the wirelesscommunication terminal 201 can change the communication used between thewireless communication base station 101 from the frequency channel ch.1to the frequency channel ch.2. In changing the communication frequencychannel to the frequency channel ch.2, in the first embodiment, thewireless communication terminal 201 sends a change request 1001 to thewireless communication base station 101 on the frequency channel ch.1 asshown in FIG. 16. In the case of the communication based on IEEE 802.11,the change request 1001 is a unicast management frame (subsequent frames1002 to 1004 are also unicast management frames), and after the wirelesscommunication base station 101 send an ack frame because the changerequest 1001 is a unicast frame addressed to the wireless communicationbase station 101, it may accept the channel change request of thewireless communication terminal 201 as is. On the other hand, in FIG.16, the wireless communication base station 101 sends a channel changeresponse 1002 in which the wireless communication terminal 201 isnotified of the response (in this case, permission) for the changerequest while the response is inserted in the status code subfield.Therefore, the wireless communication terminal 201 can confirm whetheror not the wireless communication base station 101 accepts the changerequest to change the communication frequency channel to the frequencychannel ch.2. The wireless communication terminal 201 will make itselfcapable to perform transmission and reception on the frequency channelch.2 when determining that the wireless communication base station 101accepts the change request to change the communication to the frequencychannel ch.2 (by receiving an ack frame to the change request frame, orby receiving a successful change response frame if it is expected to bereceived). If the wireless communication terminal 201 can only performtransmission and reception on a single frequency channel, the frequencyconversion circuit 6 of FIG. 2 is switched to the frequency channelch.2, and parameter change and circuit switching in the MAC unit 2 andthe PHY unit 4 are also performed according to the communication systemsupported with the frequency channel ch.2.

It is assumed that the wireless communication base station 101 has atransmission queue which accommodates frames to transmit in eachfrequency channel. The transmission queue is provided in the accesscontrol unit for PHY1 31 of FIG. 3 for the frequency channel ch.1, andthe transmission queue is provided in the access control unit for PHY232 of FIG. 3 for the frequency channel ch.2.

After receiving the channel change request 1001, the wirelesscommunication base station 101 stops the transmission of at least thedata frame to the wireless communication terminal 201 on the frequencychannel ch.1. After transmitting the necessary frame(s). (This isbecause it is necessary for the wireless communication base station 101to send the ack frame (control frame) or the response frame (managementframe) for the channel change.), the wireless communication base station101 may stop the transmission of all the frames to the wirelesscommunication terminal 201. During the period when stopping thetransmission to the wireless communication terminal 201, the wirelesscommunication base station 101 moves frames addressed to the wirelesscommunication terminal 201 from the transmission queue for the frequencychannel ch.1 to the transmission queue for the frequency channel ch.2.

When the access control unit for PHY1 31 of FIG. 3 controls frametransmission on the frequency channel ch.1, a system for stopping anaccess operation here can be one way to simply stop the frametransmission on the frequency channel ch.1 (transmission of all theframes will be stopped on the frequency channel ch.1 by this). WhenCSMA/CA is used as an access system, the transmission can be alsostopped by making the wireless communication base station 101 in asimilar situation like it detects the wireless medium to be busy. Or theaccess itself may be cancelled to stop the operation of passing out theframe from the transmission queue (located in the access control unitfor PHY1 31 of FIG. 3). For a system for stopping not all the frametransmission on the frequency channel ch.1 but only the transmissionaddressed to the wireless communication terminal 201, the destinationaddress (address 1 field) of frames can be confirmed at the exit of thetransmission queue on the frequency channel ch.1 and the access isprocessed if it is not to the wireless communication terminal 201, butthe frame is moved to the transmission queue for the frequency channelch.2 if it is to the wireless communication terminal 201. Alternatively,the access may be continued until a framer for the wirelesscommunication terminal 201 comes to the head (exit) of the transmissionqueue, and the access operation may be stopped when a frame for thewireless communication terminal 201 comes to the head of thetransmission queue.

Similarly, the wireless communication terminal 201 stops transmission ofat least the data frames after transmission the change request 1001 (thetransmission queue in the MAC unit 2 of FIG. 2 and the access controlunit for PHY are involved in stopping the transmission).

When the wireless communication terminal 201 becomes ready to conductcommunication on the frequency channel ch.2, the wireless communicationterminal 201 sends a channel change completion notification 1003 to thewireless communication base station 101 as can be seen from FIG. 16.Therefore, the wireless communication base station 101 can recognizethat the wireless communication terminal 201 can conduct communicationon the frequency channel ch.2. Additionally, as shown in FIG. 16, thewireless communication base station 101 may send a channel changecompletion response 1004 as a response to the channel change completionnotification 1003 in order to notify the wireless communication terminal201 that it has received the channel change completion notificationrelating to. After taking these steps, transmission of (data) frames onthe frequency channel ch.2 is started between the wireless communicationbase station 101 and the wireless communication terminal 201.

When receiving the channel change completion notification 1003, thewireless communication base station 101 re-starts the transmission of(data) frames to the wireless communication terminal 201 on thefrequency channel ch.2. Alternatively, after transmission the channelchange completion response 1004, the wireless communication base station101 may re-start transmission of (data) frames to the wirelesscommunication terminal 201 on the frequency channel ch.2.

Here, instead of the channel change completion notification 1003, thewireless communication terminal 201 may send on the frequency channelch.2 an acknowledgement frame, or a delivery confirmation response frameto the group of frames received from the wireless communication basestation 101 on the frequency channel ch.1. For example, a block ackmechanism, in which a control frame called a Block Ack Request (BAR)frame is used as a delivery confirmation request frame and a controlframe called a Block Ack (BA) frame is used as a delivery confirmationresponse frame, is defined in IEEE 802.11. The target data frames areQoS frames in which the QoS Control item is added as to the MAC headerportion. A Traffic Identifier (TID) indicating the traffic type isinserted in the QoS Control item. After the block ack mechanism is setup with another wireless communication terminal (including a wirelesscommunication base station), a wireless communication terminal(including a wireless communication base station) which receives dataframes having the same TID notify the partner wireless communicationterminal which is a transmitter of the data frames by a BA frame of thedelivery confirmation information on the data frames sent from thepartner wireless communication terminal within the range and having thecorresponding TID requested by the BAR frame from the partner wirelesscommunication terminal (there is also an implicit BAR system in whichtransmission of a BAR frame is omitted). Such mechanism can be appliedhere. For example, it is assumed that the wireless communication basestation 101 has set up the use of the block ack mechanism relating toTID=3 with the wireless communication terminal 201, and it is assumedthat the wireless communication terminal 201 receives a series of dataframes of TID=3 from the wireless communication base station 101 on thefrequency channel ch.1. After the frequency channel is changed to thefrequency channel ch.2, the wireless communication terminal 201 sendsthe delivery confirmation information retained for the wirelesscommunication base station 101 as a BA frame to the wirelesscommunication base station 101. Even if the wireless communicationterminal 201 does not receive the BAR frame from the wirelesscommunication base station 101, the wireless communication terminal 201may send the BA frame when the frequency channel is changed to thefrequency channel ch.2 and when it can send frames. The wirelesscommunication terminal 201 may send the same contents as those alreadysent to the wireless communication base station 101 on the frequencychannel ch.1, namely, the wireless communication terminal 201 mayretransmit the frame while the frequency channel from the frequencychannel ch.1 to the frequency channel ch.2. In the case where theoperation in which the wireless communication base station 101 stops thetransmission of data to the wireless communication terminal 201 isdelayed while the wireless communication terminal 201 moves from thefrequency channel ch.1 to the frequency channel ch.2, the wirelesscommunication terminal 201 may not be able to receive some frames fromthe wireless communication base station 101 due to the channel change.In such cases, by transmitting the delivery confirmation response frame,the wireless communication base station 101 can recognize the state inwhich the change in the wireless communication terminal 201 to thefrequency channel ch.2 is completed and the wireless communicationterminal 201 is ready to communicate in the frequency channel ch.2 whileconfirming which data frames are received by the wireless communicationterminal 201. Even if the wireless communication base station 101 doesnot deal with the operation of stopping the data transmission, thewireless communication base station 101 can deal with lost data byreceiving the change completion notification using a BA frame. When thewireless communication base station 101 sends not only frames of TID=3but also data frames of TID=4 to the wireless communication terminal 201on the frequency channel ch.1, desirably the wireless communicationterminal 201 sends BA frames for the data frames of TID=3 and TID=4 whencompleting the change of the frequency channel to the frequency channelch.2. In the case where the wireless communication terminal 201 receivesdata frames in plural series under the block ack mechanism from thewireless communication base station 101 because the set up is performedby exchanging management frames such as an ADDBA Request frame and anADDBA Response frame for each TID in order to use the block ackmechanism, it is desirable to send all the BA frames which have blockack set up (even if the wireless communication terminal 201 receives noframe of the corresponding TID from the wireless communication basestation 101 to send a delivery confirmation response). When the BAframes are sent instead of the change completion notification on thefrequency channel ch.2, if the BA frames are aggregated in one physicalpacket and sent (sent in aggregation format). The wireless communicationbase station 101 can process the BA frames as a single channel changecompletion notification. Based on the BA frame or the BA frames, thewireless communication base station 101 can recognize which data frameshave to be retried and retransmit those data frames to the wirelesscommunication terminal 201 on the frequency channel ch.2.

A mechanism to control timing of changed frequency channel may beprovide when the wireless communication terminal changes the frequencychannel. For example, in FIG. 16, the wireless communication terminal201 sets a subfield in the frame body item of the channel change request1001 in order to make a notification that the communication ortransmission is started on the frequency channel ch.2 after at least thepredetermined time T1 elapses since the channel change request 1001 issent. The value T1 in this subfield is a time enough for the wirelesscommunication terminal 201 to switch to the frequency channel ch.2. Thewireless communication terminal 201 sets a timer to the predeterminedtime T1 when the transmission of the channel change request 1001 iscompleted (the completion time can be recognized by a primitive signalcalled PHY_TXEND.confirm defined in IEEE 802.11, which is used by thePHY unit 4 to notify the MAC unit 2 of the time). The timer continuouslyworks even while the wireless communication terminal 201 switches to thefrequency channel ch.2, and the wireless communication terminal 201 getsaccess to the medium on the frequency channel ch.2 after thepredetermined time T1 elapses. This is performed by an operation, inwhich the frame transmission from the transmission queue fortransmission data located in the MAC unit 2 of the wirelesscommunication terminal 201 is released after the predetermined time T1elapses from the time when the transmission of the channel changerequest 1001 is completed and gets access to the medium on the frequencychannel ch.2. Or by an operation, in which the access control unit forPHY in the MAC unit 2 performs the recognition similar to therecognition that the wireless medium is busy for at least thepredetermined time T1 since the transmission of the channel changerequest 1001 is completed and performs the recognition similar to therecognition that the wireless medium becomes idle after thepredetermined time T1 elapses.

Alternatively, the time enough for the wireless communication terminal201 to switch to the frequency channel ch.2 may be counted from thereception of the channel change response 1002, which is a response frameand written as the predetermined time T1 in the frame body item of thechannel change request 1001 and sent to the wireless communication basestation 101. The wireless communication terminal 201 sets a timer to thepredetermined time T1 when the reception of the channel change response1002 is completed (the completion time can be recognized by a primitivesignal called PHY_RXEND.indication defined in IEEE 802.11, which is usedby the PHY unit 4 to notify notifies the MAC unit 2 of the time). Thetimer continuously works even while the wireless communication terminal201 switches to the frequency channel ch.2, and the wirelesscommunication terminal 201 gets access to the medium on the frequencychannel ch.2 after the predetermined time T1 elapses. The access systemis similarly performed as described previously.

Alternatively, when a notification of the time enough for the wirelesscommunication terminal 201 to switch to the frequency channel ch.2 ismade as the predetermined time T1 by the channel change request 1001,and the wireless communication base station 101 receives thenotification, it may notify the wireless communication terminal 201 of achannel change time T2 necessary for the wireless communication basestation 101 by the channel change response 1002 when (the wirelesscommunication base station 101) accepts the channel change request. Thewireless communication base station 101 stops transmission to thewireless communication terminal 201 for the channel change time T2 aftertransmitting the channel change request response 1002, and starts accessfor transmission to the wireless communication terminal 201 on thefrequency channel ch.2 after the channel change time T2. The wirelesscommunication terminal 201 moves to the frequency channel ch.2 duringthe channel change time T2 after receiving the channel change requestresponse 1002, and may start access on the frequency channel ch.2 afterthe channel change time T2 elapses. The wireless communication basestation 101 determines the channel change time T2 such that the channelchange time T2 satisfies a time necessary for the wireless communicationbase station 101 to prepare frames addressed to the wirelesscommunication terminal 201 to be sent on the frequency channel ch.2 (thetime required to move the frames addressed to the wireless communicationterminal 201 from the transmission queue for the frequency channel ch.1to the transmission queue for the frequency channel ch.2) and such thatthe channel change time T2 is not shorter than the predetermined time T1given by the wireless communication terminal 201. Therefore, asufficient switching time can be negotiated between the wirelesscommunication base station 101 and the wireless communication terminal201 to start the communication on the frequency channel ch.2.

Alternatively, instead of inserting the time (T1, or T1 and T2) for thechannel change in the frame relating to the channel change, it may beinserted in a frame for set up (for example, in the association process)to start communication between the wireless communication terminal 201and the wireless communication base station 101 (for example, by makingthe notification as a capability in the association request frame oralso inserting the time in the association response frame and performingthe negotiation), or the time may be used while not inserted in theframe because the time necessary for the channel change is uniquelydetermined (for example, defined as a MIB value in IEEE 802.11).Alternatively, instead of describing a specific value for the channelchange time, a unit parameter may be defined and the moving time may berecognized based on the unit parameter. For example, the parametercorresponding to the actual moving time is defined so as to be set to400 μs when the channel change time is indicated as “1” or to be set to1.5 ms when the channel change time is indicated as “2”. Alternatively,the notification can be made based on an interval of beacons (beaconinterval) on the frequency channel ch.2. In the case of beaconinterval=2, when the beacon is received twice or when the expectedbeacon transmission timing (corresponding to Target Beacon TransmissionTime (TBTT) in IEEE 802.11) is passed twice on the frequency channelch.2, the wireless communication terminal 201 may send the channelchange completion notification 1003 on the frequency channel ch.2 or maydirectly start communication on the frequency channel ch.2 withouttransmitting the channel change completion notification 1003.

In the system for making the notification of the time T1, the wirelesscommunication base station can previously recognize how long thetransmission to the wireless communication terminal 201 should bestopped. Therefore, the channel change completion notification 1003 madeby the wireless communication terminal 201 and the associated response1004 performed by the wireless communication base station 101 may beomitted. Alternatively, the wireless communication base station 101which can deal with the one-way request of the channel change time (T1)from the wireless communication terminal 201 may send the pending framesaddressed to the wireless communication terminal 201 based on thechannel change completion notification 1003 which is sent from thewireless communication terminal 201 on the frequency channel ch.2 afterthe time T1 elapses.

During the series of frame exchanges from the request 1001 to theresponse 1004, in the case where the wireless communication terminal 201cannot receive the frames 1002 and 1004 when the transmission of theframes 1002 and 1004 from the receiver side is expected, thecorresponding request frame 1001 or the notification frame 1003 may besent to the wireless communication base station 101 again after acertain fixed time elapses.

When the wireless communication base station 101 receives the channelchange request 1001 from the wireless communication terminal 201 (andsends the channel change response 1002 for permitting the channel changerequest 1001), the wireless communication base station 101 changes the“channel used” column of FIG. 14 corresponding to the wirelesscommunication terminal 201 from the frequency channel ch.1 to thefrequency channel ch.2, recognizes the information corresponding to thefrequency channel ch.2 in the pieces of information relating to thewireless communication terminal 201 by FIG. 14, that is, recognizes thatthe wireless communication terminal 201 supported IEEE 802.11a on thefrequency channel ch.2 by FIG. 14, and conducts the communication withthe wireless communication terminal 201 in the frequency channel ch.2using IEEE 802.11a (although the wireless communication base station 101supports both IEEE 802.11a and IEEE 802.11n). Thus, in the firstembodiment, the wireless communication base station 101 shares andmanages the connection information on the wireless communicationterminals over different frequency channels.

(Effect)

Thus, the wireless communication base station announces or notifieswhere another supported frequency channel exists and which communicationsystem is used on a certain frequency channel, so that the wirelesscommunication terminal which performs the transmission and reception onthe current frequency channel can recognize the information on anotherfrequency channel. During the connection set up, the wirelesscommunication terminal notifies the wireless communication base stationof its supporting communication systems including those on otherfrequency channels, so that the wireless communication base station canretain the supported communication systems by the wireless communicationterminal whose connection is permitted, along with the identifier.Therefore, when the wireless communication terminal moves to anotherfrequency channel which the wireless communication base stationsupports, the wireless communication base station already recognizes thesupported communication systems by the wireless communication terminalon the new channel, so that the communication can be continued. In suchcases, it is not necessary to terminate the connection once and restartthe set up to communicate on the changed frequency channel by exchangingconnection information again.

During the connection set up the match in the connection informationbetween the wireless communication terminal and the wirelesscommunication base station can be assured by the response frame sentfrom the wireless communication base station in response to the requestframe from the wireless communication terminal.

For the announcement or notification of the communication system, therecognition system of the communication systems among many systems canbe easily matched between the wireless communication base station andthe wireless communication terminal by indicating specific types ofcommunication standards and types of the extending systems in acommunication standard.

When the wireless communication base station permits the connection ofthe wireless communication terminal, the management number allocated tothe wireless communication terminal is retained as the identifier of thewireless communication terminal in the connection management table.Therefore, the wireless communication base station can identify thewireless communication terminals and easily manage the wirelesscommunication terminals using the unique identifiers.

The wireless communication base station has a queue in whichtransmission frames are stored for each frequency channel, and theframes addressed to the wireless communication terminal are transferredto the corresponding transmission queue of the new frequency channelwhen the wireless communication terminal makes the frequency channelchange request. Therefore, the wireless communication base station cansend the frames addressed to the wireless communication terminal on theappropriate frequency channel in which the communication is conductedeven when the wireless communication terminal moves between thefrequency channels.

The wireless communication base station starts communication with thewireless communication terminal on the changed frequency channel after afixed time elapses since the wireless communication base station permitsthe frequency channel change request from the wireless communicationterminal, so that a delay can be granted in order for the wirelesscommunication base station and the wireless communication terminal toprepare to start communication on the changed frequency channel. Thefixed time is set not shorter than the time necessary for the wirelesscommunication terminal to change the frequency channel, so thattransmission of the frame can be started after the wirelesscommunication terminal is assured to be in the receivable state on thechanged frequency channel. When the time required to change frequencychannel is obtained from the wireless communication terminal before thechange to another frequency channel is permitted, the time required bythe wireless communication terminal to change frequency channel iscorrectly recognized by the wireless communication base station, and thecommunication with the wireless communication terminal can be scheduledto start on the changed frequency channel after at least the timerequired to change frequency channel elapses, so that a degree ofcertainty can be enhanced for the securement that the wirelesscommunication terminal is in the receivable state on the changedfrequency channel. The fixed time is set not shorter than the timenecessary to move the frames addressed to the wireless communicationterminal between the queues in the wireless communication base station,so that the frames addressed to the wireless communication terminal canbe securely sent to the wireless communication terminal on the changedfrequency channel. By determining the time to start communicationbetween the wireless communication base station and the wirelesscommunication terminal on the changed frequency channel through theframe exchange in consideration of the above-described effects, thestart of the communication can be securely after the wirelesscommunication base station and the wireless communication terminal areprepared to conduct communication on the changed frequency channel.

When the wireless communication terminal sends the retained deliveryconfirmation information to the wireless communication base stationafter moving to another frequency channel, while the wirelesscommunication base station can confirm which frame is received by thewireless communication terminal, the wireless communication base stationcan also recognize the state that the wireless communication terminalhas completed the frequency channel change and became ready tocommunicate.

When the wireless communication base station makes the announcement ornotification of the bandwidth of another frequency channel, the wirelesscommunication terminal can determine whether or not another frequencychannel has the bandwidth in which the wireless communication terminalcan conduct communication, and the communication on the transferredfrequency channel can be secured. By the wireless communication basestation providing the information that the bandwidth of anotherfrequency channel is an integral multiple of at least 2 to the wirelesscommunication terminal, the wireless communication terminal can easilydetermine whether or not another frequency channel has the bandwidth inwhich the wireless communication terminal can conduct communication, anda communication system using bandwidth extension can be also easilyrealized.

Thus, in the first embodiment, the communication can efficiently beconducted while the plural frequency channels or plural communicationsystems are switched.

Second Embodiment

In a second embodiment, the description will be made centering on anaspect that differs with the first embodiment. The second embodimentdiffers from the first embodiment in that the notification ofinformation including a modulation and coding scheme with which thewireless communication base station and the wireless communicationterminal are supported is made, while the notification of only thestandard is made in the first embodiment.

FIG. 17 is a view explaining that the wireless communication basestation 101 of the second embodiment makes the notification that IEEE802.11a/n is used as the information about the frequency channel ch.2when transmitting the beacon on the frequency channel ch.1, and makesthe notification of a corresponding transmission rate in using the IEEE802.11a on the frequency channel ch.2 and a corresponding Modulation andCoding Scheme (MCS) in using the IEEE 802.11n on the frequency channelch.2.

FIG. 18 shows a transmission rate defined by IEEE 802.11a. In a BPSK(Binary Phase Shift Keying) modulation, there is a transmission rate of6 Mbps, which is half of the coding rate, and a transmission rate of 9Mbps, which is three-fourths of the coding rate. In QPSK (QuadraturePhase Shift Keying) modulation, there is a transmission rate of 12 Mbps,which is half of the coding rate, and a transmission rate of 18 Mbps,which is three-fourths of the coding rate. In 16-QAM (QuadratureAmplitude Modulation) modulation, there is a transmission rate of 24Mbps, which is half of the coding rate, and a transmission rate of 36Mbps, which is three-fourths of the coding rate. In 64-QAM modulation,there is a transmission rate of 48 Mbps, which is two-thirds of thecoding rate, and a transmission rate of 54 Mbps, which is three-fourthsof the coding rate. The transmission rates of 6 Mbps, 12 Mbps, and 24Mbps are required for the transmission and reception in the modulationsupported with IEEE 802.11a. The table of FIG. 18 shows the transmissionrates in the case where the basic 20-MHz channel bandwidth is used, thatis, in the case of the 20-MHz channel spacing. The transmission rate ishalved in the case of the 10-MHz channel spacing operated at“half-clock”, and the transmission rate is quartered in the case of the5-MHz channel spacing operated at “quarter-clock”. The transmissionrates of 6 Mbps, 12 Mbps, 24 Mbps are required for the transmission andreception in the case of 20 MHz, that is, the transmission rates of 3Mbps, 6 Mbps, and 12 Mbps are required for the transmission andreception in the case of the 10-MHz channel spacing, and thetransmission rates of 1.5 Mbps, 3 Mbps, and 6 Mbps are required for thetransmission and reception in the case of the 5-MHz channel spacing. Theinformation on the channel spacing is inserted as a regulatory class inthe country information element, and the information is inserted in thebeacon frame or the probe response frame. In IEEE 802.11a, the wirelesscommunication terminal (including the wireless communication basestation) notifies the other terminal (including the wirelesscommunication base station) as a supported rates element (or as anextended supported rates element when the pieces of information cannotbe accommodated in the supported rates element) that the wirelesscommunication terminal can perform the transmission and reception at acertain transmission rate and that the wireless communication terminalcan receive at a certain transmission rate while the pieces ofinformation are inserted in the frame body item of the frame(association request and association response) which is exchanged in theassociation process. In order to indicate that the transmission andreception are required at a certain transmission rate as BSS and thatthe reception can be performed at a certain transmission rate, thesupported rates element is also inserted in the beacon frame and theprobe response frame, and the supported rates element is sent asrequired information in the BSS to the wireless communication terminal.The information in forming the BSS on the frequency channel ch.2 is alsoannounced when the announcement that IEEE 802.11a can be used on thefrequency channel ch.2 is made by the beacon on the frequency channelch.1, and the information is also announced when the announcement thatIEEE 802.11a can be used on the frequency channel ch.2 is made by theprobe response on the frequency channel ch.1.

FIG. 19 shows a relationship between an MCS defined in IEEE 802.11n andthe transmission rate in the 20-MHz channel bandwidth (all therelationships are not described, but the relationships from MCS index 10are omitted). The MCSs are classified by the MCS index, and a supportedMCS set item indicates which MCS can be sent or received by the wirelesscommunication terminal (including the wireless communication basestation). The wireless communication terminal notifies the otherterminal (including the wireless communication base station) of thesupported MCS set item while the supported MCS set item is inserted inthe frame body item of the frame (association request and associationresponse) which is exchanged in the association process. The supportedMCS set item is also inserted in the beacon frame and the probe responseframe in order to inform the wireless communication terminal which MCScan be received or sent by the wireless communication base station. InIEEE 802.11n, which MCS is supported as a BSS (that is, which MCS can besent and received) is indicated as basic MCS set fields inserted in thebeacon frame and the probe response frame. In IEEE 802.11n, therelationship between MCS and the transmission rate is not unique, unlikeIEEE 802.11a, but the transmission rate is obtained by adding theinformation on the channel bandwidth (20 MHz is a mandatory and 40 MHzis an option). The announcements of the pieces of information on thesupported MCS set item and the basic MCS set item used in IEEE 802.11non the frequency channel ch.2 are also made when the announcement thatIEEE 802.11n can be used on the frequency channel ch.2 is made by thebeacon on the frequency channel ch.1. As described above, when theinformation on the channel bandwidth on the frequency channel ch.2 canalso be recognized by making the notification with the beacon on thefrequency channel ch.1, or when the information on the channel bandwidthon the frequency channel ch.2 can also be recognized by uniquedetermination with the channel identifier on the frequency channel ch.2,the wireless communication terminal 201 can previously recognize on thefrequency channel ch.1 the transmission rate which can be used by thewireless communication base station 101 when the transmission andreception are performed on the frequency channel ch.2 using IEEE802.11n.

On the other hand, in setting the connection with the wirelesscommunication base station 101 on the frequency channel ch.1, using theassociation request frame, the wireless communication terminal 201 makesthe notification that wireless communication terminal 201 is supportedwith IEEE 802.11a on the frequency channel ch.2 and the notificationthat the transmission and reception can be performed at a certaintransmission rate and the reception can be performed at a certaintransmission rate when IEEE the 802.11a is used on the frequency channelch.2 by inserting the information on the supported rates element on thefrequency channel ch.2.

For example, when the wireless communication terminal 201 sends theassociation request frame on the frequency channel ch.1 using IEEE802.11g, the wireless communication terminal 201 makes the notificationof the supported rate element information that the transmission andreception can be performed at the transmission rates of 6 Mbps, 12 Mbps,and 24 Mbps and the reception can be performed at the transmission ratesof 36 Mbps and 54 Mbps on the frequency channel ch.1, and the wirelesscommunication terminal 201 makes the notifications that the wirelesscommunication terminal 201 is supported with IEEE 802.11a on thefrequency channel ch.2, and makes the notification of the supportedrates element information that the transmission and reception can beperformed at the transmission rates of 6 Mbps, 12 Mbps, and 24 Mbps, andthat the reception can be performed at the transmission rates of 36 Mbpsand 54 Mbps on the frequency channel ch.2. It is assumed that anotherwireless communication terminal 202 makes the notification of pieces ofsupported rates element information that the wireless communicationterminal 202 can perform the transmission and reception at all thetransmission rates of 6 Mbps, 9 Mbps, 12 Mbps, 18 Mbps, 24 Mbps, 36Mbps, 48 Mbps, and 54 Mbps by IEEE 802.11g on the frequency channel ch.1and IEEE 802.11a on the frequency channel ch.2, it is assumed that thewireless communication terminal 202 makes the notification of thesupported MCS set item information that MCSs 0 to 32 can be sent andreceived by IEEE 802.11n on the frequency channel ch.2 and MCSs 33 and34 can be received, and it is assumed that the wireless communicationterminal 202 currently conducts the communication with the wirelesscommunication base station 101 on the frequency channel ch.2. In suchcases, a connection management table of FIG. 20 is used instead of theconnection management table of FIG. 14A. The transmission rate which canbe received by at least the wireless communication terminal 201 is usedwhen the wireless communication base station 101 performs thetransmission to the wireless communication terminal 201 at the sendableand receivable transmission rate, and the transmission rate which can bereceived by at least the wireless communication terminal 202 is usedwhen the wireless communication base station 101 performs thetransmission to the wireless communication terminal 202. For example,when the wireless communication base station 101 cannot perform thetransmission at the transmission rate of 54 Mbps, necessary andsufficient information may be inserted in the connection management listin consideration of the capability of the wireless communication basestation 101 such that the transmission rate of 54 Mbps is eliminatedfrom the fields of FIG. 20.

It is assumed that the information inserted in the beacon or proberesponse frame from the wireless communication base station 101 isshared by IEEE 802.11g on the frequency channel ch.1 and IEEE 802.11a onthe frequency channel ch.2 on the side of the wireless communicationterminal 201, it is assumed that the transmission and reception can beperformed at the transmission rates of 6 Mbps, 12 Mbps, 24 Mbps, and 36Mbps, and it is assumed that the reception can be performed at thetransmission rates of 9 Mbps, 18 Mbps, and 48 Mbps. In such cases, aconnection management table of FIG. 21 is produced instead of theconnection management table of FIG. 15 of the first embodiment. Thewireless communication terminal 201 sends the frame addressed to thewireless communication base station 101 at the sendable and receivabletransmission rate of the wireless communication terminal 201 using thetransmission rate which can be received by at least the wirelesscommunication base station 101. Referring to FIG. 20, the wirelesscommunication terminal 201 cannot perform the transmission at thetransmission rates of 9 Mbps, 18 Mbps, and 48 Mbps. Therefore, inconsideration of the capability of the wireless communication terminal201, necessary and sufficient information may be inserted in theconnection management list such that the transmission rates of 9 Mbps,18 Mbps, and 48 Mbps are eliminated from the fields of FIG. 21.

In the second embodiment, the supported rates element information whichcan be used in IEEE 802.11a and the IEEE 802.11a supported informationare inserted in the supported MCS set item information which can be usedin IEEE 802.11n and the IEEE 802.11n supported information.Alternatively, the frequency channel ch.2 is the 5 GHz bandwidth, thefrequency channel ch.2 is supported with the IEEE 802.11 standard(including the extended system) (or that the frequency channel ch.2 issupported with the IEEE 802.11 standard is not shown when expected asalready-known information), and the supported rates element informationand the supported MCS set item information may be inserted while theIEEE 802.11a supported information and the IEEE 802.11n supportedinformation are not inserted. That is, it is understood that thetransmission rate which can be used in IEEE 802.11a is shown only whenthe supported rates element information is recognized while thefrequency channel ch.2 is supported with the IEEE 802.11 standard in the5 GHz bandwidth, and it is understood that MCS which can be used in IEEE802.11n only when the supported MCS set item information is recognizedwhile the frequency channel ch.2 is supported with IEEE 802.11 standardin the 5 GHz bandwidth.

When the information is shared by the frequency channels, theannouncement and notification of the shared information may commonly bemade, and the pieces of information can be organized on the connectionmanagement table. For example, in connection management tables of FIGS.20 and 21, because IEEE 802.11a is equal to IEEE 802.11g in thesupported rates element information, the announcement and notificationare made such that the supported rates element information is applied tothe frequency channels ch.1 and ch.2 as the one piece of supported rateselement information, and the fields of the connection management tableof FIG. 20 may be unified.

In the case where the wireless communication terminal 201 sends thechange request 1001 for changing the frequency channel to the frequencychannel ch.2, the wireless communication base station 101 confirmswhether or not the wireless communication terminal 201 deals with thetransmission rate/MCS whose transmission and reception are requested onthe frequency channel ch.2 and the transmission rate/MCS in which atleast the reception is requested with respect to the fields of thewireless communication terminal 201 using the connection managementtable of FIG. 20. When the wireless communication terminal 201 dealswith the transmission rate/MCS whose transmission and reception arerequested by the wireless communication base station 101 on thefrequency channel ch.2 and the transmission rate/MCS in which at leastthe reception is requested, the wireless communication base station 101sends the channel change response 1002 for permitting the change requestto the frequency channel ch.2 to the wireless communication terminal201. When the wireless communication terminal 201 does not deal with oneof the transmission rate/MCS whose transmission and reception arerequested by the wireless communication base station 101 on thefrequency channel ch.2 and the transmission rate/MCS in which at leastthe reception is requested, the wireless communication base station 101notifies the wireless communication terminal 201 that the change requestto the frequency channel ch.2 is rejected using the channel changeresponse 1002.

(Effect)

Thus, the announcement and notification including the modulation andcoding scheme are made as the communication system used in anotherfrequency channel. Therefore, the wireless communication base stationand the wireless communication terminal can specifically recognize thelevel of the communication system with which the other party of thecommunication can deal with, and the appropriate transmission system canbe selected according to the other party of the communication. Thewireless communication terminal notifies the wireless communication basestation of the receivable communication system of the wirelesscommunication terminal, so that the selection range of communicationsystem addressed to the wireless communication terminal from thewireless communication base station can be widened when the receivablecommunication system differs from the sendable communication system andparticularly when the receivable communication system is larger than thesendable communication system in the range. The wireless communicationterminal notifies the wireless communication base station of thereceivable and sendable communication system of the wirelesscommunication terminal. Therefore, the wireless communication basestation can perform the transmission by the receivable communicationsystem of the wireless communication terminal, the recognition of thesendable communication system from the wireless communication terminalcan be used as the information in performing adaptive control, and thecommunication system of the frame sent from the wireless communicationterminal can be narrowed to facilitate the wireless communication basestation to deal with the reception system.

The modulation and coding scheme which can be used on another frequencychannel in the wireless communication terminal whose connection ispermitted on a certain frequency channel is retained along with theidentifier of the wireless communication terminal. Therefore, when achange request to another frequency channel is received from thewireless communication terminal, the wireless communication base stationcan determine whether or not the modulation and coding scheme which canbe used by the wireless communication terminal satisfies the usecondition on another frequency channel. When the modulation and codingscheme satisfies the use condition on another frequency channel, thecommunication with the wireless communication terminal on anotherfrequency channel can surely be secured, and the wireless communicationterminal can be moved between the frequency channels with which thewireless communication base station is supported without tentativelyterminating the connection with wireless communication terminal.

Third Embodiment

In a third embodiment, the description will be made centering on a pointthat differs from the second embodiment. The third embodiment differsfrom the second embodiment in that while the announcement ornotification of the transmission rate and MCS is made in the secondembodiment, the announcement or notification of pieces of informationexcept for the transmission rate and MCS, that is, the announcement ornotification of information necessary for the wireless communicationterminal to conduct the communication with the wireless communicationbase station on the frequency channel ch.2 is made.

Each of IEEE 802.11a/g/n needs the information except for thetransmission rate and MCS when the data exchange is started. Forexample, the announcement or notification of various functions such asan optional function in the PHY layer and an optional function in theMAC layer is made. In the third embodiment, the wireless communicationbase station 101 sends on the frequency channel ch.1 various functionsrelating to the frequency channel ch.2 while the various functions areinserted in the beacon or probe response frame, and the wirelesscommunication terminal 201 sends the various functions while the variousfunctions are inserted in the association request frame.

For example, the notification of the beacon frame is made while piecesof information of FIG. 22 are inserted in the beacon frame in order toconfigure the BSS on the frequency channel ch.1. In FIG. 22, the piecesof information are shown in order. However, it is not always necessarythat all the pieces of information be described, and only the necessaryinformation need be described. All the pieces of information are notdescribed in FIG. 22. When receiving the probe request frame, thewireless communication base station replies to the wirelesscommunication terminal while the information similar to that of thebeacon frame is inserted in the probe response frame. The wirelesscommunication terminal obtains the information necessary to be connectedto the wireless communication base station on the frequency channel ch.1by receiving the information. In the second embodiment, the informationabout the frequency channel ch.2 is inserted with respect to thesupported rates element of FIG. 22. The HT capabilities element of FIG.22 has a configuration of FIG. 23, and includes capability informationrelating to IEEE 802.11n (High Throughput; HT). The information aboutthe frequency channel ch.2 is inserted in the supported MCS set of FIG.23. In the third embodiment, the pieces of information except for thetransmission rate and MCS relating to other frequency channels withwhich the wireless communication base station is supported are also senton the frequency channel through which the beacon and probe responseframes are sent. For example, the capability element of FIG. 22 has aconfiguration of FIG. 24, the HT capabilities element has aconfiguration of FIG. 23, and the HT information element has aconfiguration of FIG. 25. The capability element, the HT capabilitieselement, and the HT information element include the pieces ofinformation except for the transmission rate and MCS, and the capabilityelement, the HT capabilities element, and the HT information element aresent on the frequency channel ch.1 when the frequency channel ch.2 isused.

Whether or not the wireless communication base station 101 of FIG. 6 issupported with QoS is indicated by the QoS bit of the capabilityinformation item in IEEE 802.11, whether or not the wirelesscommunication base station 101 is supported with the polling and how thewireless communication base station 101 is supported with the pollingare indicated by a combination of the QoS bit, a CF-pollable bit, and aCF-poll request bit of the capability information item in IEEE 802.11,and the corresponding channel bandwidth in PHY is indicated by asupported channel width set bit in the HT cap capabilities informationitem of the HT capabilities element at PHY. These pieces of informationare inserted as the corresponding information about the frequencychannel ch.2.

When the wireless communication terminal 201 performs the frame exchangefor performing the setting on the frequency channel ch.1 in order to beconnected to the wireless communication base station 101, theinformation whose notification should be made in conducting thecommunication on the frequency channel ch.2 is inserted along with theinformation for connection on the frequency channel ch.1. For example,in IEEE 802.11, pieces of information of FIG. 26 are inserted in theassociation request frame in order to be connected to the wirelesscommunication base station on the frequency channel ch.1. In FIG. 26,the pieces of information are shown in order. However, it is not alwaysnecessary that all the pieces of information be described, and only thenecessary information need be described. All the pieces of informationare not described in FIG. 26. In the second embodiment, the informationabout the frequency channel ch.2 is inserted with respect to thesupported rates element of FIG. 26. The HT capabilities element of FIG.26 has the information of FIG. 23, and the information about thefrequency channel ch.2 is inserted with respect to the supported MCS setof FIG. 23. In the third embodiment, the pieces of information similarto that relating to another frequency channel (ch.2) with which thewireless communication terminal is supported are also sent on thefrequency channel (ch.1) through which the association request frame issent. For example, the capability element of FIG. 26 includes pieces ofinformation with the configuration of FIG. 24, the HT capabilitieselement includes pieces of information with the configuration of FIG.23, and the HT information element includes pieces of information withthe configuration of FIG. 25. These pieces of information necessary touse the frequency channel ch.2 are also inserted when the associationrequest frame is sent on the frequency channel ch.1. The associationresponse frame also includes the capability element, the HT capabilitieselement, and the HT information element in addition to the supportedrates element and the extended supported rates element. When thewireless communication base station 101 inserts the corresponding piecesof information about the frequency channel ch.2 in the associationresponse frame, the wireless communication terminal 201 is connected tothe wireless communication base station 101 on the frequency channelch.2, and can confirm an attribute of the wireless communication basestation 101 again as the information necessary to conduct thecommunication under the BSS of the wireless communication base station101. These pieces of information are retained in the connectionmanagement table of each of the wireless communication base station andthe wireless communication terminal.

For the simplest system, the information necessary to conduct thecommunication on the frequency channel ch.2 is inserted in each of thebeacon frame, the probe response frame, the association request frame,and the association response frame for the frequency channel ch.1 alongwith the information (channel identifier and, if needed, centerfrequency and channel bandwidth) relating to the frequency channel ch.2.For example, in the beacon frame, the format of the beacon frame for thefrequency channel ch.1 is inserted, the information about the frequencychannel ch.2 is inserted, and the format of the beacon frame for thefrequency channel ch.2 is inserted. The portion of the beacon frameinformation for the frequency channel ch.1 and the portion of the beaconframe information for the frequency channel ch.2 (the portion in whichthe information about the frequency channel ch.2 and the format of thebeacon frame for the frequency channel ch.2 are combined) may beseparated as the MAC frame while aggregated as the PHY frame. Theportion of the beacon frame information for the frequency channel ch.1and the portion of the beacon frame information for the frequencychannel ch.2 may be separated and sent as the MAC frame and as the PHYframe. The portion of the beacon frame information for the frequencychannel ch.1 and the portion of the beacon frame information for thefrequency channel ch.2 may be sent while dealt with as a single MACframe.

The necessary function across the frequencies may be omitted while thenotification of the optional function is made.

When the function is commonly supported across the frequency channels(for example, QoS is supported in all the frequency channels), thenotification of the function may commonly be made. When the functiondepends on the frequency channel, the notification of the function maybe made in each frequency channel.

The wireless communication base station 101 can change the providedservice by adjusting an access parameter corresponding to the traffictype of the communication existing on each frequency channel orrestricting an application used. A notification of a service policy ofthe wireless communication base station on each frequency channel may bemade by the beacon frame or the probe Response frame. The wirelesscommunication terminal (in this case, wireless communication terminal201) may determine the change of the frequency channel in considerationof the service policy on each frequency channel whose notification ismade by the wireless communication base station 101. On the other hand,the wireless communication base station 101 may determine the permissionor rejection of the channel change request from the wirelesscommunication terminal 201 based on whether or not the service policycan be maintained on the changed frequency channel. For example, whenthe wireless communication base station 101 can predict that thewireless communication terminal 201 is moved onto the frequency channelch.2 to restrict the AV transmission bandwidth (throughput) on thefrequency channel ch.2, the wireless communication base station 101rejects the change request to the frequency channel ch.2 of the wirelesscommunication terminal 201. During the channel change request, thewireless communication terminal 201 notifies the wireless communicationbase station 101 of the service used on the changed frequency channel,and the wireless communication base station 101 may determine thepermission or rejection after checking the service against the supportservice on the changed frequency channel. For example, in the case wherethe frequency channel ch.2 is provided for the purpose of AVtransmission in the wireless communication base station 101, when thewireless communication terminal 201 notifies the wireless communicationbase station 101 to perform VoIP transmission in the change request tothe frequency channel ch.2, the wireless communication base station 101rejects the request because the frequency channel ch.2 is not used forthe AV transmission.

(Effect)

The wireless communication base station and the wireless communicationterminal notify each other of the information on each function in thecommunication system necessary to perform the connection and conduct thecommunication on the frequency channel except for the frequency channelon which the communication is currently conducted. Therefore, it is notnecessary to set each function on the frequency channel ch.2 after thewireless communication terminal is moved to another frequency channelwith which the wireless communication base station is compatible, andthe communication can immediately be started with each function.

Fourth Embodiment

In a fourth embodiment, the description will be made centering on anaspect added to the first to third embodiments. In the fourthembodiment, a notification of information necessary for the connectionon plural frequency channels with which the wireless communication basestation is supported is made in addition to the first to thirdembodiment.

FIG. 27 shows the state in which the wireless communication base station101 of the fourth embodiment sends the beacon frame on the two frequencychannels ch.1 and ch.2. In the first to third embodiments, theinformation about the frequency channel ch.2 is inserted in the beaconframe sent on the frequency channel ch.1. On the other hand, in thefourth embodiment, the beacon frame is also sent on the frequencychannel ch.2, and the information about the frequency channel ch.2 isinserted in the beacon frame. The notification of the information aboutthe frequency channel ch.1 may be made on the frequency channel ch.2.When the probe request frame is received from the wireless communicationterminal on the frequency channel ch.2, the information about thefrequency channel ch.2 is inserted when the wireless communication basestation sends back the probe response frame. The information about thefrequency channel ch.1 may be mixed in the probe response frame sent onthe frequency channel ch.2.

FIG. 27 shows only the information about the frequency channel ch.2 inthe beacon frame sent on the frequency channel ch.1. However, asdescribed above, the wireless communication terminal inserts theinformation about the frequency channel ch.1 in the beacon frame sent onthe frequency channel ch.1 in order to set the connection with thewireless communication base station 101 on the frequency channel ch.1.

Therefore, other wireless communication terminals (including thewireless communication base station) can recognize that the wirelesscommunication base station 101 is also activated on the frequencychannel ch.2, and an interference avoiding countermeasure can beexpected in other wireless communication terminals. The wirelesscommunication terminal can recognize the wireless communication basestation 101 as a connection candidate because the wireless communicationbase station 101 is activated on the frequency channel ch.2.

On the other hand, when the wireless communication base station 101 doesnot accept the new connection of the wireless communication terminal onthe frequency channel ch.2 (the acceptance of the connection request islimited to the frequency channel ch.1, and the connection request isaccepted on the frequency channel ch.2 only by the channel change fromthe frequency channel ch.1), the frame which is not the beacon frame isnot sent back in response to the probe request frame as the frame inwhich the notification of the information about the frequency channelch.2 is made on the frequency channel ch.2, and the information on theBSS may be sent back by another frame in response to a similar frame.That is, the subtype item frame according to embodiments of theinvention which is not recognized by a conventional wirelesscommunication terminal (hereinafter referred to as “legacy terminal”) isused. For example, in the IEEE 802.11 wireless LAN standard, althoughthe legacy terminal and the wireless communication terminal (includingthe wireless communication base station) of the fourth embodimentrecognize the frame having the subtype item of {B4,B5,B6,B7}={0,0,0,1}as the beacon frame, a new subtype item which is different from thesubtype item of {B4,B5,B6,B7}={0,0,0,1} is defined as the managementframe whose BSS information is announced on the frequency channel ch.2.One of the reserved subtype fields which are not defined in the IEEE802.11 wireless LAN standard stage with which the legacy terminal issupported is used (for the sake of convenience, the new subtype item isreferred to as subtype 1). Therefore, when receiving the managementframe of the new subtype 1, the wireless communication terminal of thefourth embodiment recognizes that the management frame of the newsubtype 1 announces the BSS information instead of the beacon frame onthe frequency channel ch.2, and that the new connection is not acceptedon the frequency channel ch.2. When the management frame of the newsubtype 1 sent on the frequency channel ch.2 indicates that the newconnection is accepted on the frequency channel ch.1, the wirelesscommunication terminal 201 can be moved to the frequency channel ch.1 tostart the exchange of the authentication frame and association frame forsetting the connection with the wireless communication base station 101.The legacy terminal cannot find the wireless communication base station101 because the legacy terminal does not receive the beacon frame, andthe legacy terminal cannot recognize the management frame of the newsubtype 1 even when receiving the management frame of the new subtype 1.Therefore, when the MAC unit performs the reception processing, thelegacy terminal determines that the management frame of the new subtype1 is the frame which cannot be recognized by filtering in the subtypeitem, cancels contents of the frame body item (that is, even if thesubtype 1 is received, the legacy terminal does not recognize thesubtype 1 as the connection candidate unlike the case in which thebeacon is received), and performs common processing when the legacyterminal can recognize the frame. In the common processing, adetermination as to whether or not setting of NAV is made from theaddress item unit and the duration/ID item of the MAC header portion, ora determination of whether the wireless communication terminal whichsends the frame from the power management bit (written in Pwr Mgt ofFIG. 8) of the Frame Control item of the MAC header portion is in apower saving mode or an active mode (in this case, the wirelesscommunication base station 101 which is always in the active mode). As aresult, the legacy terminal does not try the connection with thewireless communication base station 101. When a subtype 2 is used on thefrequency channel ch.2 instead of the probe request frame while asubtype 3 is used instead of the probe response frame, the wirelesscommunication base station 101 does not send the probe response frame onthe frequency channel ch.2 even if the wireless communication basestation 101 receives the probe request, the legacy terminal does notobtain the information on BSS from the wireless communication basestation 101 on the frequency channel ch.2, and does not try theconnection because the legacy terminal cannot find the wirelesscommunication base station 101. However, the wireless communicationterminal 201, which is the wireless communication terminal of the fourthembodiment, can obtain the BSS information about the frequency channelch.2 because the wireless communication base station 101 replies to themanagement frame of the subtype 2 using the management frame of thesubtype 3. When the new connection is accepted on the frequency channelch.1 while the information about the frequency channel ch.1 is insertedin the management frame of the subtype 3, the wireless communicationterminal 201 can be moved to the frequency channel ch.1 to start theexchange of the authentication frame and association frame for settingthe connection with the wireless communication base station 101. Becausethe frame which cannot be recognized by the legacy terminal is used, thelegacy terminal cannot recognize that the wireless communication basestation 101 is operated on the frequency channel ch.2, and cannotperform the connection on the frequency channel ch.2. On the other hand,in the wireless communication terminal of the fourth embodiment, theconnection on the frequency channel ch.2 can be restricted such that thewireless communication base station 101 is detected and connected usingthe new frame such as the subtypes 1, 2, and 3 on the frequency channelch.2.

(Effect)

Thus, the announcement and notification of the communication system ormodulation and coding scheme used in another frequency channel are madeon another frequency channel, so that other wireless communication basestations or wireless communication terminals which are receivable onanother frequency channel can recognize what communication system ormodulation and coding scheme is used on another frequency channel by thewireless communication base station.

Other wireless communication base stations and wireless communicationterminals can take the interference avoiding countermeasure by usingsuch recognition.

In the wireless communication terminal, the recognition can make thewireless communication base station the candidate of the wirelesscommunication base station to be connected.

The connection can be restricted on the other frequency channel by theframe according to embodiments of the invention which cannot berecognized by the conventional wireless communication terminal.

Fifth Embodiment

In a fifth embodiment, the description will be made centering on anaspect added to the fourth embodiment. In the fifth embodiment, thefollowing point is added to the fourth embodiment. That is, the samewireless communication base station straddles the plural frequencychannels when the wireless communication base station makes anotification of the information necessary for the connection on pluralfrequency channels with which the wireless communication base station iscompatible.

(In the Case where Addition is Realized by BSSID)

(In the Case of a Single BSSID)

For example, in the IEEE 802.11 wireless LAN standard, the BSS includesa certain wireless communication base station and a wirelesscommunication terminal connected thereto, the BSS has an identifierBSSID (Basic Service Set IDentification), and usually the BSSID islocated in the MAC address of the wireless communication base station.The wireless communication base station having the configuration of FIG.3 may have one BSSID as the MAC address. In such cases, the informationabout the frequency channel ch.2 is inserted in the beacon frame sent onthe frequency channels ch.1 and ch.2 as shown in FIG. 28, and the commonBSSID is inserted in order to indicate that the beacon frames are senton the different frequency channels from the same wireless communicationbase station.

In the IEEE 802.11 wireless LAN standard, when the wirelesscommunication base station sends the beacon frame, the BSSID is insertedin the item of the address 3 located in the MAC header of FIG. 7. One ofthe systems is to insert the same 48-bit value of the BSSID in thebeacon frames of the frequency channels ch.1 and ch.2.

In such cases, when the wireless communication terminal performs summaryprocessing of the information obtained by scanning the frequencychannel, it is necessary to simultaneously retain the informationobtained on which frequency channel. In the IEEE 802.11 wireless LANstandard, when the scanning is performed, the information on each BSS issummarized as BSS description, SME is notified of the BSS description,SME determines which BSS is connected, and the frame exchange isperformed in order to set the actual connection in the MAC layer. In thefifth embodiment, on which frequency channel the information is obtainedcan be recognized such that the identifier of the frequency channel isadded as the BSS description as shown in FIG. 29.

(In the Case of Plural BSSIDs)

Usually, a BSSID is uniquely determined from the MAC address in thewireless communication base station. Alternatively, in the wirelesscommunication base station having the configuration of FIG. 3, thedifferent frequency channels and associated access control units may beunified to allocate a different BSSID to each frequency channel. Thatis, a BSSID is set at BSSID1 when the frame is sent through the PHY1access control unit 31, the PHY1 processing unit 33, and the firstfrequency conversion circuit 35 of FIG. 3, and a BSSID is set at BSSID2when the frame is sent through the PHY2 access control unit 32, the PHY2processing unit 34, and the second frequency conversion circuit 36 ofFIG. 3. The plural BSSIDs are managed by the MAC layer management unit30 which commonly manages the plural frequency channels. The value of aBSSID may be specified outside the MAC layer management unit 30, forexample, by an external input, or the value of a BSSID may uniquely beallocated by the MAC layer management unit 30.

Here, BSSID1, which is the BSSID on the frequency channel ch.1, isinserted in the item of address 3 of the MAC header in the beacon frameon the frequency channel ch.1, the frame body item is notified that theBSSID on the frequency channel ch.2 is BSSID2 along with the informationabout the frequency channel ch.2, and BSSID2, which is the BSSID on thefrequency channel ch.2, is inserted in the item of address 3 of the MACheader in the beacon frame on the frequency channel ch.2. When thewireless communication terminal 201 changes the frequency channel fromthe frequency channel ch.1 to the frequency channel ch.2, the beaconframe on the frequency channel ch.2 is received, and the confirmationthat the beacon frame is sent by the same wireless communication basestation can be made from the information whose notification is made onthe frequency channel ch.1. The information about the frequency channelch.1 and that the frequency channel ch.1 having BSSID of BSSID1 areinserted in the frame body item of the beacon frame on the frequencychannel ch.2, and the notification of the information about anotherfrequency channel and BSSID used on another frequency channel may bemade by the beacon frame sent on each frequency channel. This case isshown in FIG. 30. The pieces of information about other frequencychannels are not limited to the order of description of FIG. 30.

In the IEEE 802.11 wireless LAN standard, in addition to a BSSID, asystem identifier of an SSID (Service Set Identifier) also exists asshown in FIGS. 22, 26, and 29. In an LLC including plural BSSs, SSID isan identifier of an ESS (Extended Service Set) which is recognized asone BSS. For example, SSID is an identifier indicating a system of thesame operator (in some cases, the same service is provided). The samevalue of the SSID may be used in either of the two examples (one BSSIDand plural BSSIDs). The value of the SSID may be changed according tothe frequency channels ch.1 and ch.2, when a difference is provided inthe support service such that different traffic types are supported bythe frequency channels ch.1 and ch.2, such that a higher priority isgiven to different traffic type (which can be performed by adjusting theaccess parameter), or such that the supported application is restricted(for example, frequency channel ch.2 is used only for the videotransmission).

(Effect)

Thus, the notification that the same wireless communication base stationis operated on the plural frequency channels can be made by making thenotification of the identifier of the wireless communication basestation on another frequency channel.

The wireless communication terminal, in which the communication with thewireless communication base station is conducted on a certain frequencychannel, and the communication with the wireless communication basestation is conducted again on another frequency channel, recognizes thewireless communication base station. Therefore, the frame can be sent tothe wireless communication base station.

Sixth Embodiment

In a sixth embodiment, the description will be made centering on anaspect differing from the fifth embodiment. The sixth embodiment differsfrom the fifth embodiment in that, while the same wireless communicationbase station is indicated using a BSSID in the fifth embodiment, anidentifier which is different from the BSSID is separately provided toindicate the same wireless communication base station.

For example, the legacy terminal which is supported with the IEEE 802.11wireless LAN standard does not recognize the additional information ofthe sixth embodiment, and cannot be expected to perform the informationmanagement system according to embodiments of the invention. Asdescribed in the fifth embodiment, the pieces of information aresummarized as the BSS Description in each BSSID. Therefore, when thenotification system of the fifth embodiment in which the single BSSID isused is performed, the legacy terminal cannot distinguish the pieces ofinformation on the beacon frame or probe response frame received fromthe same wireless communication base station on the plural frequencychannels, and cannot recognize the pieces of information about thedifferent frequency channels of the sixth embodiment. When theinformation is raised from the PHY layer to the MAC layer, the legacyterminal performs the desired processing (such that an informationelement is extracted and reflected on the subsequent processing in MAC)for the information in which the frame type (up to the subtype level) isrecognized and the item position at which the information isaccommodated in the frame is uniquely determined (a item start point isfixed and a item length is fixed) or the information in which, even inthe information in which the item position is not determined, theelement ID can be recognized in the configuration (FIG. 23) includingthe item accepting the identifier (Element ID), the item indicating theitem length, and the information item having the variable length. Theportion which cannot be recognized by the system is allocated in the MAClayer and the portion is not reflected on the subsequent processing.Accordingly, the legacy terminal can understand the beacon frame and theprobe response frame, can also understand the item of address 3 when theitem of address 3 is used in the notification system in which the singleBSSID is used, and receives the same frame and the same information onthe plural channels. The operation of the legacy terminal may becometroublesome unless such situations are accounted for in the design.

Therefore, in the sixth embodiment, while different values (like thesecond-half example of the fifth embodiment) are allocated to BSSIDsused in the frequency channel (unlike the second-half example of thefifth embodiment in which the notification of the BSSID on anotherchannel is made in the frame body fields of the beacon and proberesponse frames), new fields which can be understood by the wirelesscommunication terminal of the sixth embodiment are provided in the framebody fields of the beacon and probe response frames. For example, asshown in FIG. 31, a common identifier called Multi-Channel ID (MCID) isinserted in the frame body fields of the beacon and probe responseframes which are sent on each of the frequency channels ch.1 and ch.2.Because the legacy terminal cannot recognize an MCID, the legacyterminal does not perform the processing of the information even if thelegacy terminal receives the frame, and therefore such trouble is notgenerated. The wireless communication terminal of the sixth embodimentcan understand the MCID, and can recognize the same wirelesscommunication base station when the MCID has the common item value evenif the beacon and probe response frames having different BSSIDs arereceived on different frequency channels. The wireless communicationterminal 201 which is moved to the frequency channel ch.2 recognizes thebeacon frame and probe response frame which are sent on the frequencychannel ch.2 of the wireless communication base station 101 from theMCID, and obtains the BSSID (BSSID 2) which is used on the frequencychannel ch.2 by the wireless communication base station 101 from thebeacon frame and probe response frame, and BSSID2 is used in thesubsequent communication. Alternatively, an MCID may be inserted in theMAC header portion of the frame which is sent by the wirelesscommunication base station 101 and the wireless communication terminal201. An MCID may be inserted only on the frequency channel ch.2, or anMCID may be inserted in the frame which is sent on all the targetfrequency channels of the embodiments (in this case, frequency channelsch.1 and ch.2). The wireless communication terminal 201 can recognizethe frame having an MCID as one which is sent from the wirelesscommunication base station 101.

(Effect)

The notification that the same wireless communication base stationstraddles the plural frequency channels is made in the item differentfrom the item indicating the identifier of the wireless communicationbase station which can conduct the communication only on the singlefrequency channel. Therefore, when the wireless communication terminalconnectable only to the wireless communication base station which canconduct the communication only on the single frequency channel receivesthe notification, the wireless communication terminal can recognize thewireless communication base station as another one, and can be connectedto the wireless communication base station. When the wirelesscommunication terminal connectable to the wireless communication basestation which can conduct the communication on plural frequency channelsreceives the notification, the wireless communication terminal canrecognize the wireless communication base station as the same one, andcan be connected to the wireless communication base station.

Seventh Embodiment

In a seventh embodiment, the description will be made centering on anaspect added to the third to sixth embodiments. In the seventhembodiment, the following point is added to the third to sixthembodiments. That is, the frame is simultaneously sent on all thesendable frequency channels when the wireless communication base station101 sends a frame such as a broadcast frame and a multicast frame inwhich a destination address becomes a group address.

In the case where the configuration of FIG. 6 is adopted, because thewireless communication base station 101 is simultaneously sendable onthe frequency channels ch.1 and ch.2 (even if the simultaneoustransmission is not actually performed due to the different conditionthat the access right is obtained), the wireless communication basestation 101 sends the group address frame on the frequency channels ch.1and ch.2. In other words, the group address frame is simultaneously senton all the sendable and receivable frequency channels, because thefrequency channels ch.1 and ch.2 are the simultaneously receivablefrequency channels for the wireless communication base station 101.

Usually, in the IEEE 802.11 wireless LAN standard, a item indicating theorder of the frame is provided when the frame is sent. The order isinserted in the sequence control item of FIG. 7. Particularly, thesequence control item is divided into a fragment number item and asequence number item as shown in FIG. 32. The sequence number itemindicates a sequence number of an MSDU (MAC Service Data Unit) or MMPDU(MAC Management Protocol Data Unit), that is, the order of the frame.MSDU is a frame which is produced from data transferred from the upperlevel of the MAC layer, for example, LLC layer, and becomes a dataframe. An MMPDU is a frame which is produced to move a managementprotocol of the MAC layer, and becomes a management frame. A counter ofmodulo-4096 is allocated to the sequence number in each TrafficIdentifier (TID) or reception terminal when the wireless communicationterminal distinguishes the types of QoS in the IEEE 802.11 wireless LANstandard, and the counter is incremented by one. The management frameand the QoS frame are not distinguished from each other when the groupaddress frame or the non-QoS frame is sent. A counter of modulo-4096 isallocated to the group address frame or the non-QoS frame in addition tothe plural counters, and the counter is incremented by one every timethe MSDU or MMPDU frame is sent. In the case of a transmission mode inwhich the wireless communication terminal does not distinguish the typesof QoS, one counter of modulo-4096 is incremented by one in each oneMSDU or MMPDU. The fragment number item of FIG. 32 indicates thefragment number, that is, the order of the fragment when one MSDU orMMPDU is sent while divided into fine units having short frame lengthscalled fine fragments (referred to as fragment processing). The one MSDUor MMPDU can be divided up to 64 fragments in the fragment processing.The values 0 to 63 are allocated to the fragment number fields in eachfragment. In the case where the same MSDU or MMPDU is fragmented, thesame value is inserted in the sequence number fields, and the order ofthe fragment is written in the fragment number field.

In the IEEE 802.11 wireless LAN standard, when the wirelesscommunication terminal (including the wireless communication basestation) receives the frame, the wireless communication terminalconfirms whether or not the frame is addressed to itself from theaddress item of the MAC header in the reception operation. Because theframe is sent while the direct address to connect terminal is describedin the address 1 item of the MAC header, the wireless communicationterminal compares whether or not the item of address 1 is identical tothe MAC address of itself. When the item of address 1 is identical tothe MAC address of the wireless communication terminal, the wirelesscommunication terminal determines that the frame is addressed to itself.In the case where the selection retransmission system is used, thefragmented frames are arranged in the order of the fragment, the frameis converted into the form of MSDU/MMPDU which has no fragment torearrange the order of the frames received in the order of the sequencecontrol item when one MSDU/MMPDU is completed (referred to as defragmentprocessing), the frame is transferred to the higher level of the MAClayer, for example, the LLC layer or the management frame is transferredto the MAC layer management unit 30, and the desired operation isperformed based on the determination through an SME if needed. When theframe having the same sequence number is received from the same wirelesscommunication terminal (the frame having the same fragment number in thecase of the frame to which the fragment processing is performed), theframe is allocated because of the overlapping reception. In the casewhen the frame requires the ack response, the ack frame is sent afterSIFS elapses since the reception irrespective of the overlapping. Whenthe wireless communication terminal determines that the frame is notaddressed to itself, while the frame is allocated, that the media isbusy in the MAC layer is recognized, that is, the virtual carrier senseis invoked only for a time written in duration/ID item in which the NAV(Network Allocation Vector) is set based on the duration/ID item of FIG.7 (described by Dur/ID in FIG. 7).

The group address is described in the item of address 1 in the case ofthe group address frame. In the IEEE 802.11 wireless LAN standard, whenreceiving the group address, the wireless communication terminal, whichis connected to the wireless communication base station through theassociation process, extracts BSSID (the item of address 3 of FIG. 7 inthe case of the management frame, or the item of address 2 of FIG. 7 inthe case where the wireless communication base station sends the dataframe to the wireless communication terminal thereof) described in theMAC header, and the wireless communication terminal determines whetheror not the BSSID described in the MAC header is identical to the BSSIDof the BSS to which the wireless communication terminal belongs. Whenthe BSSID described in the MAC header is identical to the BSSID of theBSS to which the wireless communication terminal belongs (the wirelesscommunication terminal further determines whether or not the BSSIDdescribed in the MAC header is a multicast frame including the wirelesscommunication terminal in the case of the multicast frame, and when theBSSID described in the MAC header is the multicast frame), the desiredprocessing (frame body item portion is extracted and transferred to thehigh-order layer or the MAC layer management unit 30, and a desiredoperation is performed through an SME if needed) is performed in the MAClayer. When the BSSID described in the MAC header is not identical tothe BSSID of the BSS to which the wireless communication terminalbelongs, the frame is allocated. In the case of the group address frame,the ack frame is not sent after SIFS, even if the group address includesthe wireless communication terminal. Similarly to the unicast frame, theframe is allocated when the frame having the same sequence number isreceived from the same wireless communication terminal. In the casewhere the same group address is received from plural wirelesscommunication terminals by a mesh-like configuration, because thetransmission address which generates the data and the item correspondingto the sequence number on a mesh network are provided in the frame, thepieces of information are combined to determine whether or not theframes overlap each other. The frame is allocated when the framesoverlap each other.

In the case where the single BSSID of the fifth embodiment indicates thesame wireless communication base station, the wireless communicationterminal 201 receives the group address frame 1 on the frequency channelch.1. When the wireless communication terminal 201 is transferred to thefrequency channel ch.2 (because the wireless communication base station101 obtains the access right) to receive the group address frame 1again, because the fields of the frames in which BSSID is described inthe MAC header are identical to the MAC address of the wirelesscommunication base station 101, and the frames have the same sequencenumber. Therefore, the group address frame 1 which is received later onthe frequency channel ch.2 is allocated. In the case where theconventional wireless communication terminal performs the channelchange, even if the frames are sent on plural frequency channels fromthe same wireless communication base station, the wireless communicationterminal cannot recognize that the frames are sent on plural frequencychannels from the same wireless communication base station when thenotification of the frame is made by an unsupported item. Accordingly,in the seventh embodiment, the item in which the already existing BSSIDis described and the item in which the sequence number is described areused according to the already existing application, so that even theconventional wireless communication terminal which is unsupported withembodiments of the invention can recognize the overlapping of the groupaddress frames and dispose the group address frame by the MAC layer.

The wireless communication terminal 201 receives the group address frame1 on the frequency channel ch.1, when the system of the fifth embodimentfor making the notification (announcement) of BSSID, used on anotherfrequency channel, on the frequency channel while plural BSSIDs areprovided is used. When the wireless communication terminal 201 istransferred to the frequency channel ch.2 (because the wirelesscommunication base station 101 obtains the access right) to receive thegroup address frame 1 again, because the wireless communication terminal201 previously recognizes the BSSID used on the frequency channel ch.2although the two frames differ from each other in the item in which theBSSID is described in the MAC header, the group address frame 1 receivedon the frequency channel ch.2 also becomes the processing target in theMAC layer. Because of the same sequence number, the wirelesscommunication terminal 201 recognizes the same group address frame sentfrom the same wireless communication base station, and disposes thegroup address frame 1 received later on the frequency channel ch.2. Inthe case where the MCID of the sixth embodiment is used, the MCID issimilarly inserted in the group address frame (for example, the item inwhich the MCID is inserted in the frame body item is provided in thecase of the management frame, the item in which the MCID is inserted inthe MAC header portion is provided in the case of the data frame).Therefore, the wireless communication terminal 201 can recognize thesame group address frame sent from the same wireless communication basestation, and can dispose the group address frame 1 received later on thefrequency channel ch.2. On the other hand, in the above-describedsystems, even if the same group address is received on the pluralfrequency channels, the legacy terminal cannot recognize that the groupaddresses are sent from the same wireless communication base station andthat the group address can be allocated because of the overlapping.Accordingly, it is necessary that the group address be identified andallocated by a layer higher than the MAC layer on the wirelesscommunication terminal side, or it is necessary that the legacy terminalon the wireless communication base station side changes the frequencychannel such that the same group address is not sent in an overlappingmanner when the legacy terminal is connected to the wirelesscommunication base station on the changed frequency channel.

As described above, in the case where the wireless communicationterminal changes the frequency channel, in order to reduce theoverlapping group address, desirably the wireless communication basestation recognizes the time the wireless communication terminal changesthe frequency channel, and performs the transmission after the frequencychannel change. In the case where the frequency channel movements ofplural wireless communication terminals overlap each other, desirablythe wireless communication base station waits for completion of all themovements of the wireless communication terminals. Additionally, for thegroup address frame, in the IEEE 802.11 wireless LAN standard, sometimesthe wireless communication terminal which is in the power saving modeneeds to recognize the timing of the receivable state to perform thetransmission. Therefore, the group address frame is sent inconsideration of such need. As described above, in the case where thelegacy terminal changes the frequency channel, the wirelesscommunication base station cannot previously recognize when thefrequency channel is changed and when the legacy terminal is connectedto the wireless communication base station on the new frequency channel.Therefore, when the wireless communication base station 101 recognizesthat the legacy terminal is moved from the frequency channel ch.1 to thefrequency channel ch.2 and connected to the wireless communication basestation 101, in order that the control is performed in the MAC layersuch that the group address frame is not sent to the legacy terminalagain, the multicast address frame addressed to the conventionalwireless communication terminal and the multicast address frameaddressed to the wireless communication terminal of the seventhembodiment are separately provided, and the group address frameaddressed to the legacy terminal and the group address frame addressedto the wireless communication terminal of the seventh embodiment aresent while distinguished from each other such that the information whichis already sent to the legacy terminal on the frequency channel ch.1 issent on the frequency channel ch.2 using the multicast address frameaddressed to the wireless communication terminal of the seventhembodiment. In such cases, the transmission may be performed on thefrequency channel ch.2 after a predetermined time elapses (for example,after at least a channel change time expected in the legacy terminal).The frequency channel on which the connection of the legacy terminal ispermitted is limited to one frequency channel (for example, thefrequency channel ch.1), and the connection of the legacy terminal maybe rejected on another frequency channel (for example, the frequencychannel ch.2) to prevent the generation of such a problem.

(Effect)

Thus, the frames addressed to the plural wireless communicationterminals are sent on all the sendable and receivable frequencychannels. Therefore, the destination wireless communication terminalwhose frequency channel is possibly moved can surely receive the frame.Additionally, in transmitting the frame, it is not necessary that thewireless communication base station correctly specify the connectedfrequency channel including the movement of the frequency channel toconnect wireless communication terminal, and a processing load can bereduced.

When the same frames addressed to the plural wireless communicationterminals are sent on the plural frequency channels, the same value isinserted in the item indicating the order of the delivery number.Therefore, in the case where the transmission timing is shifted amongthe plural frequency channels, the overlapping can be recognized, evenif the wireless communication terminal moved between the frequencychannels or the wireless communication terminal which can perform thereception on the plural frequency channels receives the same packets onthe plural frequency channels.

Eighth Embodiment

In an eighth embodiment, the description will be made centering on anaspect added to the third to seventh embodiments. In the eighthembodiment, the point that the same wireless communication base stationmakes an announcement and a notification of a channel usage rate onanother simultaneously usable frequency channel is added to the third toseventh embodiments.

The case in which the wireless communication base station 101 makes theannouncement or notification of the information about the frequencychannel on the frequency channels ch.1 and ch.2 as shown in FIG. 30 willbe described below. The wireless communication base station 101 makesthe announcement or notification of the channel usage rate of thefrequency channel ch.2 on the frequency channel ch.1 while the usagerate on the frequency channel ch.2 is included in the beacon frame orprobe response frame as the information about the frequency channelch.2. On the contrary, the announcement or notification of the channelusage rate of the frequency channel ch.1 may be made on the frequencychannel ch.2 while the channel usage rate on the frequency channel ch.1is included in the information about the frequency channel ch.1.

The channel usage rate is a time in which a frequency channel isoccupied for a constant observation period. In the mechanism in whichthe transmission is performed using CSMA, the wireless communicationterminal (including the wireless communication base station) adapts acompetition system in which the transmission is performed when thewireless communication terminal determines that the frequency channel isempty. CSMA/CA (Carrier Sense Multiple Access with Carrier Avoidance) isa system in which, in order that the wireless communication terminalsare prevented from simultaneously getting access to the frequencychannel to collide with each other in the empty time, the wirelesscommunication terminal gets access to the frequency channel after thewireless communication terminal waits for a constant fixed time and arandom time while the frequency channel is empty. In the case of theIEEE 802.11 wireless LAN standard in which CSMA/CA is used, thedetermination as to whether or not the frequency channel is empty ismade by a Clear Channel Assessment (CCA) mechanism which recognizes thestate of the wireless medium in the PHY layer and the status of thevirtual carrier sense in the MAC layer. In the PHY layer, the MAC layeris notified of CCA=BUSY when a reception electric power having apredetermined level is detected on the frequency channel, and the MAClayer is notified of CCA=IDLE when the reception electric power is ofthe predetermined level or less (in FIG. 2, the notification signal issent from the PHY unit 4 to MAC unit 2). For example, the receptionelectric power of the predetermined level is −82 dBm when a preambleportion located in the head of the PHY packet can be detected, and is−62 dBm when the preamble portion cannot be detected. The sum of sets ofthe period during which the CCA signal from the PHY layer is BUSY andthe time described in the duration/ID item of the frame which is notaddressed to the MAC layer (that the medium recognizes BUSY for the timeto stop the transmission is referred to as “NAV is set”, and themechanism which recognizes the medium as BUSY even if CCA is actuallyIDLE in the PHY layer is referred to as “virtual carrier sense”) iscomputed in the MAC layer, the sum of sets is recognized as thefrequency channel being occupied, and an exclusive period of the sum ofsets is recognized as the frequency channel being empty. Accordingly,because the observation as to whether or not the frequency channel isoccupied is made when the transmission is performed on the frequencychannel, statistical processing can be performed on the information tocompute the time the frequency channel is occupied for the constantobservation period. When the beacon interval during which the beaconframe is sent is fixed (when CSMA/CA is used, the time the beacon frameis actually sent on the frequency channel does not become constant), thefrequency channel occupied time observed for the beacon interval may beindicated, or the frequency channel occupied time observed for severalbeacon intervals may be divided by the beacon interval (normalized bythe beacon interval) to indicate an average occupied time.

The channel usage rate is a data amount which is sent per constant timeby the wireless communication base station. An average data amount perunit time such as the beacon interval may be indicated after themeasurement is performed for the predetermined time as described above.

The channel usage rate is a time necessary to actually obtain the accessright since the access request is generated, when the wirelesscommunication base station gets access to the wireless medium perpredetermined time to perform the transmission. An average access timeper unit time such as the beacon interval may be indicated after themeasurement is performed for the predetermined time as described above.

In the eighth embodiment, the frequency channel usage rate is basicallydescribed by the system for computing the statistical processing whenthe wireless communication base station performs the channel access. Thewireless communication base station is notified of the result observedby the wireless communication terminal connected to the wirelesscommunication base station, and the information may be used as thechannel usage rate. In such cases, the information on the observationresult is collected from plural wireless communication terminalsconnected to the wireless communication base station and the statisticalprocessing may be performed on the information to use the information asthe frequency channel usage rate.

The wireless communication terminal 201 obtains the information on thechannel usage rate from the wireless communication base station 101 onanother frequency channel, and determines whether or not the wirelesscommunication terminal 201 is transferred to another frequency channel.For example, when the channel occupied rate of the frequency channelch.2 is shorter than that of the currently used frequency channel ch.1,the wireless communication terminal 201 determines that desirably thewireless communication terminal 201 is transferred to the frequencychannel ch.2 to conduct the communication.

The wireless communication terminal 201 computes the statistics tocompare the channel usage rate of the frequency channel ch.1 to thechannel usage rate of the frequency channel ch.2. Here, when thewireless communication base station 101 obtains the channel usage rateof the frequency channel ch.1 on the frequency channel ch.1 and thechannel usage rate of the frequency channel ch.2 on the frequencychannel ch.2, the wireless communication terminal 201 can compare thestates of the frequency channels ch.1 and ch.2 as the information fromthe wireless communication base station 101.

(Effect)

Thus, the wireless communication base station notifies the wirelesscommunication terminal of the channel usage rate of another frequencychannel. Thus, the information can be provided to the wirelesscommunication terminal which determines whether or not the wirelesscommunication terminal transferred to another frequency channel, and thewireless communication terminal determines whether or not the wirelesscommunication terminal transferred to another frequency channel based onthe information, so that the communication can be secured on thetransferred frequency channel. The channel usage rate is indicated bythe channel occupied rate, the average transmission data amount per unittime, or the average time to obtain the access right, so that thespecific index can be obtained when the wireless communication terminalmakes the determination.

Ninth Embodiment

In a ninth embodiment, the description will be made centered on pointsadded to the first to eighth embodiments. In the ninth embodiment, thefollowing point is added to the first to eighth embodiments. That is,the wireless communication base station includes security informationset between the wireless communication base station and the wirelesscommunication terminal in the connection management table used to managethe information on the connection with the wireless communicationterminal, and conducts the communication with the wireless communicationterminal with the security setting even if the wireless communicationterminal changes the frequency channel.

In the IEEE 802.11 wireless LAN standard, there are plural systems forencrypting the communication. TKIP (Temporal Key Integrity Protocol), inwhich a security level is enhanced by developing WEP or WEP based on anARC 4 algorithm, and CCMP (Counter mode with Cipher-block chainingMessage authentication code Protocol) based on AES (Advanced EncryptionStandard), which has a high level of security, can be cited as examplesof encryption systems in exchanging the data frame. WEP is divided intoa system in which 64-bit-length data is used for a secret key and asystem in which 128-bit-length data is used to strengthen the security.The communication between the wireless communication base station andthe wireless communication terminal can be encrypted when the wirelesscommunication base station and the wireless communication terminal aresupported with the common encryption system.

In the ninth embodiment, when the wireless communication terminal 201performs the connection setting for the communication with the wirelesscommunication base station 101 on the frequency channel ch.1 in theconfiguration of FIG. 6, the wireless communication terminal 201 alsoperforms a setting for the data exchange with the wireless communicationbase station 101 using TKIP. The wireless communication base station 101retains the connection management table of FIG. 33 for the connectedwireless communication terminal. In the connection management table ofFIG. 33, a item of security information is added instead of theconnection management table of FIG. 14A. When the connection settingincluding the TKIP setting is normally ended between the wirelesscommunication base station 101 and the wireless communication terminal201 (wireless communication base station 101 permits the connection withthe wireless communication terminal 201 with TKIP), the connectioninformation on the wireless communication terminal 201 is written andretained as shown in FIG. 33. When the wireless communication basestation 101 refers to the information on the wireless communicationterminal 201 retained in the connection management table, the wirelesscommunication base station 101 can understand that the wirelesscommunication terminal 201 is supported with the frequency channels ch.1and ch.2, the communication can be performed pursuant to IEEE 802.11g onthe frequency channel ch.1, the communication can be performed pursuantto IEEE 802.11a on the frequency channel ch.2, frequency channel ch.1 iscurrently used, and the communication is conducted with TKIP. In theconnection management table of FIG. 33, the wireless communication basestation 101 conducts communication with the wireless communicationterminal 202 with COMP (AES may be described instead of CCMP) becausethe wireless communication base station 101 normally ends the connectionsetting, including the CCMP setting.

The wireless communication terminal 201 sends the change request tochange the frequency channel to the frequency channel ch.2 to thewireless communication base station 101. When the wireless communicationbase station 101 permits the channel change request to the frequencychannel ch.2, the wireless communication base station 101 and thewireless communication terminal 201 conduct the communication on thefrequency channel ch.2 using TKIP, which is the encryption system set onthe frequency channel ch.1, after the wireless communication terminal201 is changed to the frequency channel ch.2. Only the item of“supported channel” of FIG. 33 is changed from the frequency channelch.1 to the frequency channel ch.2, and the information on TKIP isretained. In FIG. 33, only the name of the encryption system is retainedin the connection management table. However, when the information havingresolution higher than the name of the encryption system is required inusing the encryption system such that encryption keys are distinguishedin each wireless communication terminal even in the same encryptionsystem, obviously the information is included in the connectionmanagement table.

(Effect)

Thus, the wireless communication base station manages the securityinformation and the identifier of the wireless communication terminal,and the same security information is used on the changed frequencychannel when the wireless communication base station permits the changerequest to another frequency channel. Therefore, the communication canbe started between the wireless communication base station and thewireless communication terminal without setting the security again onthe changed frequency channel.

Tenth Embodiment

In a tenth embodiment, the description will be made centering on anaspect differing from the ninth embodiment. The tenth embodiment differsfrom the ninth embodiment in the following point. That is, while thecommunication is conducted using the same encryption system after thechannel change of the wireless communication terminal in the ninthembodiment, the wireless communication base station confirms whether ornot the wireless communication terminal is supported with the encryptionsystem on the frequency channel of the change request in receiving thechannel change request from the wireless communication terminal, thewireless communication base station permits the channel change when thewireless communication terminal is supported with the encryption system,and the wireless communication base station rejects the channel changewhen the wireless communication terminal is not supported with theencryption system.

For example, in the configuration of FIG. 6, the wireless communicationbase station 101 is supported with TKIP and CCMP on the frequencychannel ch.1. However, the wireless communication base station 101permits only the CCMP communication on the frequency channel ch.2because the communication having a higher security intensity ispermitted. The security policy, which depends on the frequency channel,may be stored in the MAC layer management unit 30 of FIG. 3 in the formof the security policy management table, or the information can bestored in an external memory, and the MAC layer management unit 30 mayaccess the external memory to confirm and refer to the information ifneeded. In such cases, when the wireless communication terminal 201sends the channel change request to the frequency channel ch.2 to thewireless communication base station 101 while the connection managementtable is in the state of FIG. 33, the wireless communication basestation 101 refers to FIG. 33 to confirm that TKIP is the currentencryption system with the wireless communication terminal 201, and thewireless communication base station 101 rejects the channel changerequest to the frequency channel ch.2 from the wireless communicationterminal 201. In transmitting the rejection of the channel changerequest as the frame to the wireless communication terminal 201, areason that the security request is not satisfied may be included in theframe. Usually, the channel change response frame is the managementframe, and notification of both the rejection and the reason of therejection is made by a item called status code in the management frameof the response system to the request when the notification of therejection is made. Therefore, the management frame may be used.

When the security policy depends on the frequency channel, the securitypolicy on another frequency channel may be announced by the beacon framewhile the security policy is included as the information about thefrequency channel, and the notification of the security policy onanother frequency channel may be made by the probe response frame whilethe security policy is included as the information about the frequencychannel. For example, in the above-described example, that the frequencychannel ch.2 is supported with the CCMP encryption system or that theCCMP encryption system is required is inserted as the information aboutthe frequency channel ch.2 in the beacon and probe response frames ofthe frequency channel ch.1. The beacon frame of FIG. 34 is sent insteadof the beacon frame of FIG. 17. On the contrary, that the frequencychannel ch.1 is supported with the TKIP and CCMP encryption systems maybe inserted as the information about the frequency channel ch.1 in thebeacon and probe response frames of the frequency channel ch.2. In thewireless communication terminal 201, as shown in FIG. 35, a item of theencryption system corresponding to each channel is provided instead ofFIG. 15 to retain pieces of operation information about the frequencychannels ch.1 and ch.2 of the wireless communication base station 101.When the notification of the encryption system which cannot berecognized by the wireless communication terminal 201 is made, thenotification may be inserted in the information. For the notification ofthe security system on another frequency channel, when the wirelesscommunication base station and the wireless communication terminal havethe same recognition (by matching of a correlation table mutuallyreferred to for the use of the encryption system), a display system suchas the security level may simply be performed.

(Effect)

Thus, the wireless communication base station recognizes the usablesecurity system of the wireless communication terminal before thewireless communication terminal makes the change request to anotherfrequency channel, and determines whether the change request ispermitted or rejected based on the usable security system when receivingthe change request to another frequency channel. Therefore, the securityof the wireless communication terminal can be retained on anotherfrequency channel. In the case where the security system needed by thewireless communication base station is not satisfied, the wirelesscommunication terminal previously recognizes the connection request ofthe wireless communication terminal which is known to be rejected onanother frequency channel, and the frequency channel occupation createdby the wasted frame exchange for the connection can be reduced. In thecase where the wireless communication base station permits the wirelesscommunication terminal to change the frequency channel to anotherfrequency channel, the information on the security system of which thewireless communication terminal notifies the wireless communication basestation can be used in the communication with the wireless communicationterminal on the changed frequency channel.

The wireless communication base station notifies the wirelesscommunication terminal of the security level needed on another frequencychannel, so that the wireless communication terminal can determinewhether or not the wireless communication terminal is supported with thesecurity system of another frequency channel while the security levelneeded on another frequency channel can be changed.

Eleventh Embodiment

In an eleventh embodiment, the description will be made centering on anaspect differing from the tenth embodiment. The eleventh embodimentdiffers from the tenth embodiment in the following point. In the tenthembodiment, the wireless communication base station rejects the channelchange request of the wireless communication terminal when theencryption system used before the channel change is not the encryptionsystem needed on the frequency channel of the change request. On theother hand, in the eleventh embodiment, in the case where the encryptionsystem used before the channel change is not the encryption systemneeded on the frequency channel of the change request, the wirelesscommunication base station permits the change request when the wirelesscommunication base station can select one of the encryption systemsneeded on the frequency channel of the change request in the usableencryption systems of the wireless communication terminal, and thewireless communication base station performs the setting of the selectedencryption system with the wireless communication terminal before thedata exchange communication is conducted on the changed frequencychannel.

Therefore, it is necessary that the wireless communication terminalpreviously notify the wireless communication base station of pluralsupported encryption systems.

In the configuration of FIG. 6, when the wireless communication terminal201 sends the connection request to the wireless communication basestation 101 on the frequency channel ch.1, the wireless communicationterminal 201 sends the information that the wireless communicationterminal 201 is supported with TKIP and CCMP to the wirelesscommunication base station 101 while the information is included in thecapability. Thus, in the wireless communication base station 101, theconnection management table for the wireless communication terminalbecomes the connection management table of FIG. 36. In the connectionmanagement table of FIG. 36, a item of the supported encryption systemis added instead of FIG. 33. FIG. 36 similarly shows the state in whichthe wireless communication terminal 202 makes the notification that CCMPis the supported encryption system of the wireless communicationterminal 202.

When the wireless communication terminal 201 and the wirelesscommunication base station 101 perform the connection setting of thecommunication in which TKIP is used on the frequency channel ch.1, thewireless communication terminal 201 may notify the wirelesscommunication base station 101 that the wireless communication terminal201 is supported with the frequency channel ch.2, that the wirelesscommunication terminal 201 is supported with a certain communicationsystem on the frequency channel ch.2, and that the wirelesscommunication terminal 201 is supported with a certain encryption systemexcept for TKIP. Alternatively, the wireless communication terminal 201initially notifies the wireless communication base station 101 only thatthe wireless communication terminal 201 is supported with TKIP for theencryption system when the wireless communication terminal 201 performsthe connection setting of the communication on the frequency channelch.1, and the wireless communication terminal 201 may additionallynotify the wireless communication base station 101 that the wirelesscommunication terminal 201 is supported with the CCMP encryption systemwhen the wireless communication terminal 201 understands that the CCMPencryption system is needed in the communication on the frequencychannel ch.2 by the beacon frame or probe response frame from thewireless communication base station 101 and when the wirelesscommunication terminal 201 determines that the notification of othersupported encryption systems should be made because of the possibilityof making the transition to the frequency channel ch.2.

When the wireless communication base station 101 receives the requestframe to change the channel to the frequency channel ch.2 from thewireless communication terminal 201, the wireless communication basestation 101 understands that only the communication with TKIP is setbetween the wireless communication base station 101 and the wirelesscommunication terminal 201. However, from the connection managementtable of FIG. 36, the wireless communication base station 101understands that the wireless communication terminal 201 is supportedwith the CCMP encryption system needed in the communication on thefrequency channel ch.2. Therefore, the wireless communication basestation 101 permits the channel change request, and performs the settingfor stating the COMP communication with the wireless communicationterminal 201 before the data frame exchange is started on the frequencychannel ch.2. In performing the setting for starting the CCMPcommunication, the CCMP setting request may be sent to the wirelesscommunication terminal while the CCMP setting request is included in thechannel change response frame. Here, the wireless communication terminal201 which receives the channel change response frame sends the framenecessary for the CCMP setting with the wireless communication basestation 101 on the frequency channel ch.1. Alternatively, the wirelesscommunication terminal 201 sends the frame necessary for the CCMPsetting on the frequency channel ch.2 after completing the movement tothe frequency channel ch.2. The wireless communication base station 101may send the CCMP setting request to the wireless communication terminal201 after the wireless communication terminal 201 is moved to thefrequency channel ch.2. Here, the wireless communication terminal 201sends the frame necessary for the CCMP setting to the wirelesscommunication base station 101 on the frequency channel ch.2.

In the eleventh embodiment, the wireless communication base station 101sends the CCMP setting request to the wireless communication terminal201 after receiving the channel change request frame from the wirelesscommunication terminal 201. Alternatively, when the wirelesscommunication base station 101 recognizes that the wirelesscommunication terminal 201 is supported with the CCMP encryption system,because the wireless communication base station 101 needs the use of theCCMP encryption system on the frequency channel ch.2, the wirelesscommunication base station 101 may send the CCMP setting request to thewireless communication terminal 201 before the wireless communicationterminal 201 sends the channel change request frame.

In the eleventh embodiment, the wireless communication base station 101makes the CCMP setting request to the wireless communication terminal201, and the wireless communication terminal 201 sends the framenecessary for the CCMP setting to the wireless communication basestation 101 in response to the CCMP setting request. Alternatively, thewireless communication terminal 201 may send the frame necessary for theCCMP setting to the wireless communication base station 101 to start theCCMP setting from the wireless communication terminal 201, when thewireless communication terminal 201 understands that the CCMP encryptionsystem is needed in the communication on the frequency channel ch.2 bythe beacon frame or probe response frame from the wireless communicationbase station 101, and when the wireless communication terminal 201determines that the notification of other supported encryption systemsshould be made because of the possibility of making the transition tothe frequency channel ch.2.

(Effect)

Thus, when the security system of the pre-change of the frequencychannel change can be used after the frequency channel is changed, theframe exchange for the resetting for using the security system after thefrequency channel change can be omitted by conducting the communicationusing the same security information. When the security system in whichthe wireless communication terminal is supported with the securitysystem needed by the wireless communication base station exists althoughthe security system of the pre-change of the frequency channel changecannot be used after the frequency channel is changed, the wirelesscommunication base station performs the setting of the security systemon the changed frequency channel between the wireless communication basestation and the wireless communication terminal, and the wirelesscommunication base station can retain the security needed on the changedfrequency channel.

Twelfth Embodiment

In a twelfth embodiment, the description will be made centered on apoint added to the first to eleventh embodiments. In the twelfthembodiment, the following point is added to the first to eleventhembodiments. That is, the wireless communication terminal notifies thewireless communication base station of the usable communication systemon another frequency channel after the wireless communication terminalis connected to the wireless communication base station.

In the configuration of FIG. 6, the wireless communication terminal 201exchanges the association frame with the wireless communication basestation 101 in order to perform the setting necessary for the connectionon the frequency channel ch.1, and the wireless communication terminal201 is ready to conduct the communication on the frequency channel ch.1.In the twelfth embodiment, a management frame of a new subtype (in thiscase, subtype 5), which is different from the association frame, isprovided to make the notification of the communication system supportedwith another frequency channel, and the wireless communication basestation 101 is notified of the communication system with which thewireless communication terminal 201 is supported on the frequencychannel ch.2 using the subtype 5. The notification of the supportedcommunication system on the frequency channel ch.2 is already made inthe association request frame, as in the above-described embodiments,and then the wireless communication terminal 201 is additionallysupported with another frequency channel, for example, the frequencychannel ch.3. In such cases, the notification of the communicationsystem of the frequency channel ch.3 may be made by the management frameof the subtype 5. The management frame of the subtype 5 is a unicastframe addressed to the wireless communication base station 101. Whenreceiving the management frame of the subtype 5, the wirelesscommunication base station 101 replies with the ack frame similar tothat of the case in which the usual unicast frame is received. Thewireless communication base station 101 writes and retains the supportedcommunication system on the frequency channel ch.2 in the item relatingto the wireless communication terminal 201 of the connection managementtable.

The wireless communication terminal 201 notifies the wirelesscommunication base station 101 of the supported communication system onthe frequency channel ch.2 before transmitting the change request to thefrequency channel ch.2 to the wireless communication base station 101.

(Effect)

Thus, after performing the connection on a certain frequency channel,the wireless communication terminal additionally makes the notificationof the usable communication system on another frequency channel. A delaycan be granted in order to prepare the notification frame relating tothe communication system which can be used on another frequency channelby the wireless communication terminal, and the communication cancontinuously be conducted with no resetting after the channel changewhile a load is reduced during the connection setting.

Thirteenth Embodiment

In a thirteenth embodiment, the description will be made centering on anaspect added to the first to eleventh embodiments. In the thirteenthembodiment, the following point is added to the first to eleventhembodiments. That is, the wireless communication terminal notifies thewireless communication base station that the compatibility is changedfor the information on the communication system which can be used onanother frequency channel, and the notification of the information onthe communication system is made in making the connection request.

In the configuration of FIG. 6, it is assumed that the wirelesscommunication base station retains a connection management table of FIG.37, and it is also assumed that the wireless communication terminal 202performs the connection setting on the frequency channel ch.1. In thethirteenth embodiment, the description will be made using the wirelesscommunication terminal 202. During the connection on the frequencychannel ch.1, the wireless communication terminal 202 notifies thewireless communication base station 101 of the supported communicationsystem on the frequency channel ch.2. When the supported communicationsystem is changed on the frequency channel ch.2, the wirelesscommunication terminal 202 notifies the wireless communication basestation 101 of the changes using a management frame of a new subtype (inthis case, subtype 6). For example, in the state of which the wirelesscommunication terminal 202 notifies the wireless communication basestation 101, the electric power is supplied, the sendable and receivablemodulation and coding scheme is MCS=0 to 32 on the frequency channelch.2 in IEEE 802.11n while the receivable modulation and coding schemeis MCS=33 and 34 on the frequency channel ch.2 in IEEE 802.11n such thatthe wireless communication terminal 202 corresponds to the fields of theconnection management table of FIG. 37. Then, the electric power supplyis eliminated, and the wireless communication terminal 202 determinesthat the wireless communication terminal 202 does not correspond to thereceivable modulation and coding scheme of MCS=33 and 34 which is a lowpower consumption measure. The wireless communication terminal 202notifies the wireless communication base station 101 that the wirelesscommunication terminal 202 does not correspond to the receivablemodulation and coding scheme of MCS=33 and 34 using the subtype 6. Thewireless communication base station 101 receives contents of the subtype6 to update the information on the proper portion relating to thewireless communication terminal 202 in the connection management table.In the wireless communication base station 101, the connectionmanagement table is updated as shown in FIG. 38. For the system in whichthe wireless communication terminal 202 notifies the wirelesscommunication base station 101 of the changes, because only a portion ofIEEE 802.11n is changed, the notification of the changed portion thatthe receivable modulation and coding scheme is eliminated may be made,or the notification of all the supported communication systems (thesendable and receivable modulation and coding scheme is MCS=0 to 32 andthe receivable modulation and coding scheme is MCS=void) relating to thefrequency channel ch.2 may be made. When the plural frequency channelshave some change in common, the notification of the frequency channel(in this case, frequency channels ch.1 and ch.2) influenced by thechange and the communication system may be made, or the notification ofthe change of the communication system may be made while the frequencychannel is omitted. In the case where the notification of the change ofthe communication system is made while the frequency channel is omitted,the wireless communication terminal 202 notifies the wirelesscommunication base station 101 of contents relating to MCS, so that thewireless communication base station 101 understands that the wirelesscommunication terminal 202 is supported with IEEE 802.11n and thereforeit is only necessary to update the retained contents on the frequencychannel ch.2.

When the supported communication system on the frequency channel ch.2has some change, the wireless communication terminal 202 notifies thewireless communication base station 101 before transmitting the changerequest to the frequency channel ch.2 to the wireless communication basestation 101.

(Effect)

Thus, when the communication system which can be used by the wirelesscommunication terminal is changed, the wireless communication terminalre-notifies the wireless communication base station of the information.Therefore, the wireless communication terminal and the wirelesscommunication base station can conduct the communication with each otherby a communication system appropriate to the communication state of thewireless communication terminal.

Fourteenth Embodiment

In a fourteenth embodiment, the description will be made centering on anaspect added to the first to thirteenth embodiments. In the fourteenthembodiment, the following point is added to the first to thirteenthembodiments. That is, the fourteenth embodiment includes an operation inthe case where the wireless communication terminal is connected to thewireless communication base station by which the information on thewireless communication terminal connected on plural frequency channelscannot be shared and managed.

In the configuration of FIG. 39, the wireless communication terminal 201can conduct the communication on both the frequency channel ch.1 and thefrequency channel ch.2. The wireless communication base station 102 maysimultaneously conduct the communication on the frequency channel ch.2,or the wireless communication base station 102 may simultaneouslyconduct the communication only on one frequency channel (in this case,frequency channel ch.1). Only the information about the frequencychannel (for example, in this case, frequency channel ch.1) is insertedin the frame (such as the beacon frame and the probe response frame)sent on the frequency channel (for example, in this case, frequencychannel ch.1). Even if the wireless communication terminal 201 sends theinformation necessary to conduct the communication on another frequencychannel (in this case, frequency channel ch.2), the wirelesscommunication base station 102 retains the information, and the wirelesscommunication base station 102 does not use the information whenconducting the communication with the wireless communication terminal201 on another frequency channel (ch.2). On the other hand, although thewireless communication base station 103 is similar to the wirelesscommunication base station 102, the frequency channel ch.1 in thewireless communication base station 102 is changed to the frequencychannel ch.2.

In such conditions, the wireless communication terminal 201 is connectedto the wireless communication base station 102 on the frequency channelch.1 to conduct the communication with the wireless communication basestation 102. It is assumed that the wireless communication terminal 201makes a request to change the frequency channel to the frequency channelch.2. The channel change request is made in consideration of thewireless communication status or the transmitting traffic requirement ofthe wireless communication terminal 201 from the result in which SMEcollects the information through the PHY layer and the MAC layer, andthe MAC layer management unit 30 is notified of the channel changerequest.

Here, the wireless communication terminal 201 recognizes that thewireless communication base station 102 cannot retain and use thecommunication information used on the frequency channel ch.2 of thewireless communication terminal 201 even if the wireless communicationbase station 102 makes the change request to the frequency channel ch.2.For example, in the case where the wireless communication base stationexerts a function of making the announcement and notification offrequency channel information which is different from the informationretaining capability between the frequency channels of the wirelesscommunication terminal, the wireless communication base station 102 canrecognize that the wireless communication base station 102 cannot retainand use the communication information used on the frequency channel ch.2of the wireless communication terminal 201, because the wirelesscommunication base station 102 does not perform the transmission whilethe information about the frequency channel ch.2 is included in thebeacon frame/probe response frame on the frequency channel ch.1. In thecase where the wireless communication base station has the informationretaining capability between the frequency channels of the wirelesscommunication terminal, the wireless communication base station 102 canrecognize that the wireless communication base station 102 cannot retainand use the communication information used on the frequency channel ch.2of the wireless communication terminal 201, when the notification of theinformation is made as the capability of the wireless communication basestation by the beacon frame/probe response frame.

The wireless communication terminal 201 switches the frequency channelto the frequency channel ch.2, and searches for the operated wirelesscommunication base station by the scan. Here, the wireless communicationterminal 201 may send a frame (in the IEEE 802.11 wireless LAN standard,the management frame is called a disassociation frame) for notifying thewireless communication base station 102 of the disconnection. Thewireless communication terminal 201 sends the frame to the wirelesscommunication base station 102, so that the wireless communication basestation 101 can suppress the retaining information amount by deletingthe information on the wireless communication terminal 201 from theconnection management table. When detecting that the wirelesscommunication base station 103 is operated on the frequency channelch.2, the wireless communication terminal 201 makes the connectionrequest to the wireless communication base station 103. When thewireless communication base station 103 permits the connection, thewireless communication terminal 201 starts the communication with thewireless communication base station 103 on the frequency channel ch.2.When detecting the plural wireless communication base stations on thefrequency channel ch.2, the wireless communication terminal 201 collectsthe pieces of information on the plural wireless communication basestations using the MAC layer management unit 30, the wireless terminalentity selects the wireless communication base station to which theconnection request is sent according to the collected pieces ofinformation, and the connection setting operation is started through theMAC layer management unit 30. For example, it is assumed that thewireless communication base station 102 is also operated on thefrequency channel ch.2 (terminal management is not shared by thefrequency channel ch.1) and it is assumed that the wirelesscommunication terminal 201 detects the wireless communication basestation 102 and the wireless communication base station 103 on thefrequency channel ch.2. Here, the wireless communication terminal 201selects the wireless communication base station to which the connectionrequest is sent in consideration of the frame receiving conditions (suchas reception electric power and interference amount) from each wirelesscommunication base station and the capability of each wirelesscommunication base station. In transmitting the connection request, thewireless communication terminal 201 notifies the wireless communicationbase station of the capability necessary to conduct the communication onthe frequency channel ch.2. According to the embodiment, examples of thenotification of the capability include the supported communicationstandard, the modulation and coding scheme, and the encryption system.The wireless communication terminal 201 may send the connection requestin the form of a reconnection request when transmitting the connectionrequest to the wireless communication base station 103 without notifyingthe wireless communication base station 102 of the disconnection (in theIEEE 802.11 wireless LAN standard, the case in which the disassociationframe is not sent). In the IEEE 802.11 wireless LAN standard, theconnection request in the form of a reconnection request becomes amanagement frame called reassociation request. The information which isbasically similar to that on the association request frame is sent inthe reassociation request frame. Additionally, notification of thepreviously connected wireless communication base station (in this case,the wireless communication base station 102) is made in thereassociation request frame. When the wireless communication basestation 103 receives the reassociation request frame from the wirelesscommunication terminal 201, and when the reassociation request frameshows that the previously connected wireless communication base stationis the wireless communication base station 102, cooperation can be madebetween the wireless communication base stations such that the wirelesscommunication base station 103 notifies the wireless communication basestation 102 that the wireless communication terminal 201 is connected tothe wireless communication base station 103, and such that the dataaddressed to the wireless communication terminal 201 which is sent tothe wireless communication base station 102 is transferred to thewireless communication base station 103. In the reassociation process,similarly to the association process, the wireless communication basestation sends the response management frame (the reassociation responseframe to the reassociation request frame).

When the wireless communication terminal 201 can detect on the frequencychannel ch.1 the wireless communication base station which is operatedon the frequency channel ch.2, desirably the wireless communicationterminal 201 is connected to the wireless communication base station onthe frequency channel ch.1 in consideration of the generation of thechannel change request to the frequency channel ch.2.

(Effect)

Thus, the wireless communication terminal is connected to the wirelesscommunication base station with which the communication can be conductedon a single frequency channel while connected to the wirelesscommunication base station with which the communication can be conductedsimultaneously on at least two frequency channels, so that options ofthe communication destination can be increased. Additionally, in thecase where the transfer request to the second frequency channel is madeeven if the wireless communication terminal is connected to the wirelesscommunication base station with which the communication can be conductedon a single frequency channel, the wireless communication terminalnotifies the wireless communication base station of the usablecommunication system on the second frequency channel to make theconnection request when searching for and detecting the wirelesscommunication base station which can be connected on the secondfrequency channel, and can be connected to the wireless communicationbase station which is operated on the second frequency channel.

Fifteenth Embodiment

In a fifteenth embodiment, the description will be made centering on anaspect to the first to thirteenth embodiments. In the fifteenthembodiment, the following point is added to the first to thirteenthembodiments. That is, the fifteenth embodiment is an operation of thewireless communication terminal when the wireless communication basestation rejects the channel change request sent from the wirelesscommunication terminal.

In the configuration of FIG. 6, the wireless communication terminal 201is connected and conducts the communication with the wirelesscommunication base station 101 on the frequency channel ch.1, and sendsthe channel change request to the frequency channel ch.2 to the wirelesscommunication base station 101. The wireless communication base station101 receives the channel change request, and rejects the channel changerequest because the wireless communication terminal 201 is not supportedwith the modulation and coding scheme needed on the frequency channelch.2, because the wireless communication terminal 201 is not supportedwith the encryption system needed on the frequency channel ch.2, orbecause the wireless communication terminal 201 cannot support thecommunication on the frequency channel ch.2 (for example, the wirelesscommunication base station 101 is already connected to many wirelesscommunication terminals). When receiving the channel change response ofthe rejection from the wireless communication base station 101, thewireless communication terminal 201 switches the frequency channel tothe frequency channel ch.2 to scanning whether or not another wirelesscommunication base station is operated on the frequency channel ch.2.Similarly to the fourteenth embodiment, the wireless communicationterminal 201 may send the frame (in the IEEE 802.11 wireless LANstandard, the disassociation frame) notifying the wireless communicationbase station 101 of the disconnection. When only the wirelesscommunication base station 101 is detected on the frequency channelch.2, the wireless communication terminal 201 can make the connectionrequest to the wireless communication base station 101 again. However,desirably the wireless communication terminal 201 detects and selectsanother wireless communication base station because the wirelesscommunication terminal 201 can expect that the connection request isrejected. In the case where the wireless communication terminal 201detects another wireless communication base station except for thewireless communication base station 101, (after the wirelesscommunication terminal 201 determines that the wireless communicationbase station is supported with the communication system needed by thewireless communication terminal 201 on the frequency channel ch.2), thewireless communication terminal 201 makes the connection request to thewireless communication base station. Similarly to the fourteenthembodiment, the wireless communication terminal 201 may send theconnection request in the form of a reconnection request (in the IEEE802.11 wireless LAN standard, a reassociation request frame) whentransmitting the connection request to the newly connected wirelesscommunication base station without notifying the wireless communicationbase station 101 of the disconnection (in the IEEE 802.11 wireless LANstandard, the case in which the disassociation frame is not sent).

In the case where the communication cannot be conducted on the frequencychannel ch.2 because only the wireless communication base station 101can be detected as the wireless communication base station suitable forthe communication on the frequency channel ch.2 or because the wirelesscommunication base station 101 rejects the connection request even ifthe wireless communication terminal 201 makes the connection request tothe wireless communication base station 101 on the frequency channelch.2 again, the wireless communication terminal 201 reviews the channelchange request, and returns to the communication on the frequencychannel ch.1 or tries the connection on another frequency channel exceptfor the frequency channel ch.2. For example, the wireless communicationterminal 201 sends the channel change request to the frequency channelch.3 to the wireless communication base station 101, when the wirelesscommunication terminal 201 recognizes that the wireless communicationbase station 101 is operated on the frequency channel ch.3 in additionto the frequency channels ch.1 and ch.2.

(Effect)

While the wireless communication terminal is connected to the wirelesscommunication base station with which the communication can besimultaneously conducted on at least two frequency channels, thewireless communication terminal searches for another wirelesscommunication base station which can be connected on the secondfrequency channel when the wireless communication base station rejectsthe channel change request to the second channel. When detecting anotherwireless communication base station, the wireless communication terminalnotifies another wireless communication base station of the usablecommunication system on the second frequency channel to make theconnection request, and can be connected to another wirelesscommunication base station operated on the second frequency channel.Therefore, options of the communicable wireless communication basestation can be increased.

Sixteenth Embodiment

In a sixteenth embodiment, the description will be made centered on anaspect added to the first to thirteenth embodiments. In the sixteenthembodiment, the following point is added to the first to thirteenthembodiments. That is, the sixteenth embodiment is an operation of thewireless communication terminal when the wireless communication terminalmakes a change request to a frequency channel which is not supported bythe wireless communication base station.

In the configuration of FIG. 6, it is assumed that the wirelesscommunication terminal 201 is supported with the frequency channelsch.1, ch.2, and ch.3 while the wireless communication base station 101can simultaneously conduct the communication on the frequency channelsch.1 and ch.2. The assumption includes not only the case in whichwireless communication terminal 201 is supported with all the frequencychannels with which the wireless communication base station 101compatible, and other frequency channels, but also the case in which thefrequency channels partially overlap such that the wirelesscommunication base station 101 is supported with the frequency channelsch.1 and ch.2 while the wireless communication terminal 201 is supportedwith the frequency channels ch.1 and ch.3.

In the fifteenth embodiment, the wireless communication terminal 201conducts the communication with the wireless communication base station101 on the frequency channel ch.1, and the frequency channel is changedto the frequency channel ch.2 with which both the wireless communicationbase station 101 and the wireless communication terminal 201 arecompatible. On the other hand, in the sixteenth embodiment, the wirelesscommunication terminal 201 changes the frequency channel to thefrequency channel ch.3 of which the wireless communication base station101 does not make the announcement or notification as the simultaneouslycommunicable frequency channel. As described above, SME makes thedetermination of the change to the frequency channel ch.3 based on thewireless communication situation or the traffic request. Because thewireless communication base station 101 does not include the frequencychannel ch.3 as the simultaneously communicable frequency channel, evenif the wireless communication terminal 201 changes the frequency channelto the frequency channel ch.3, the wireless communication terminal 201understands that the wireless communication base station 101 has noguarantee to be able to start the communication on the frequency channelch.3 without performing the resetting while retaining the information onthe connection with the wireless communication terminal 201. Therefore,the wireless communication terminal 201 switches the frequency channelto the frequency channel ch.3 to scanning whether or not anotherwireless communication base station is operated on the frequency channelch.3. Before the wireless communication terminal 201 scans whether ornot another wireless communication base station is operated on thefrequency channel ch.3, the wireless communication terminal 201 assumesthat the wireless communication terminal 201 is not reconnected to thewireless communication base station 101 on the frequency channel ch.3,and may send the frame (in the IEEE 802.11 wireless LAN standard,disassociation frame) notifying the wireless communication base station101 of the disconnection, as in the fifteenth embodiment. When thewireless communication base station is detected (when the wirelesscommunication terminal 201 determines that the wireless communicationbase station is supported with the communication system needed by thewireless communication terminal 201 on the frequency channel ch.3), thewireless communication terminal 201 makes the connection request to thewireless communication base station. Similarly to the fifteenthembodiment, the wireless communication terminal 201 may send theconnection request in the form of a reconnection request (in the IEEE802.11 wireless LAN standard, the reassociation request frame), whenmaking the connection request to the new wireless communication basestation without notifying the wireless communication base station 101 ofthe disconnection (in the IEEE 802.11 wireless LAN standard, the case inwhich the disassociation frame is not sent). When the wirelesscommunication base station 101 can be detected on the frequency channelch.3 (even if the announcement and notification of the frequencychannels ch.1 and ch.2 are not made as the simultaneously supportedfrequency channel), and when the wireless communication base station 101is supported with the communication system satisfying the need duringthe use of the frequency channel ch.3 of the wireless communicationterminal 201, the wireless communication terminal 201 makes theconnection request to the wireless communication base station 101 again.Here, the wireless communication terminal 201 sends the associationframe to the wireless communication base station 101 when thedisassociation frame has already been sent. The wireless communicationterminal 201 sends the association frame or the reassociation frame tothe wireless communication base station 101 when the disassociationframe is not sent.

In the case where the communication cannot be conducted on the frequencychannel ch.3 because the wireless communication base station suitablefor the communication on the frequency channel ch.3 cannot be detectedor because the wireless communication base station rejects theconnection request even if the wireless communication terminal makes theconnection request to the wireless communication base station on thefrequency channel ch.3, the wireless communication terminal reviews thechannel change request, and returns to the communication on thefrequency channel ch.1 or tries the connection on another frequencychannel except for the frequency channel ch.3. For example, when thewireless communication terminal 201 is also supported with the frequencychannel ch.4, the wireless communication terminal 201 scans whether ornot the appropriate wireless communication base station exists on thefrequency channel ch.4.

(Effect)

While the wireless communication terminal is connected to the wirelesscommunication base station with which the communication can besimultaneously conducted on at least two frequency channels, thewireless communication terminal searches for another wirelesscommunication base station which can be connected on the third frequencychannel when the channel change request to the third frequency channelwith which the same wireless communication station is not supported ismade. When detecting another wireless communication base station, thewireless communication terminal notifies another wireless communicationbase station of the usable communication system on the third frequencychannel to make the connection request, and the wireless communicationterminal can be connected to another wireless communication base stationoperated on the third frequency channel. Therefore, options of thecommunicable wireless communication base station can be increased.

Seventeenth Embodiment

In a seventeenth embodiment, the description will be made centered on anaspect that differs with the first to thirteenth embodiments. Theseventeenth embodiment differs from the first to thirteenth embodimentsin that the wireless communication terminal notifies the wirelesscommunication base station of the information about another frequencychannel during the connection request even if the wireless communicationbase station does not make the announcement and notification of theinformation about the communication system on another frequency channel.

In the configuration of FIG. 6, the wireless communication base station101 of the seventeenth embodiment does not insert the communicationsystem used on the frequency channel ch.2 in the beacon frame sent onthe frequency channel ch.1, and the communication system used on thefrequency channel ch.2 is not inserted in the probe response frame sentby the wireless communication base station 101 when the wirelesscommunication terminal 201 sends the probe request frame to the wirelesscommunication base station 101 (either the group address frame or theunicast frame) on the frequency channel ch.1.

Here, in the wireless communication base station 101, the identifier formaking the notification that the wireless communication base station 101is sendable and receivable on another frequency channel or that theinformation on the connection with the wireless communication terminaland the connection on another frequency channel is commonly managed maybe inserted in the beacon frame or the probe response frame. Forexample, the MCID of the sixth embodiment can be used in thisapplication.

On the other hand, the wireless communication terminal 201 notifies thewireless communication base station 101 of the communication system withwhich the wireless communication terminal 201 is supported on thefrequency channel ch.2 when making the connection request to thewireless communication base station 101 on the frequency channel ch.1.Here, the wireless communication terminal 201 determines that thewireless communication base station 101 is not the legacy wirelesscommunication base station but the wireless communication base stationof the seventeenth embodiment by inserting an MCID in the beacon frameor the probe response frame, and the wireless communication terminal 201may notify the wireless communication base station 101 of the supportedcommunication system on the frequency channel ch.2.

When the wireless communication base station 101 detects that theinformation about the communication system with which the wirelesscommunication terminal 201 is supported on the frequency channel ch.2 isincluded in the association request frame from the wirelesscommunication terminal 201, the wireless communication base station 101registers the information on the wireless communication terminal 201 inthe connection management table, and notifies the wireless communicationterminal 201 of the successful connection using the association responseframe. The notification of the successful connection is inserted in astatus code. A code indicating the permitted association requestincluding another supported frequency channel may be used as the statuscode instead of the code simply indicating that the association issuccessful. The wireless communication base station 101 may insert thecommunication system with which the wireless communication base station101 is supported on the frequency channel ch.2 in the associationresponse frame. Therefore, because the association response frameincludes the status code and the information about the frequency channelch.2 as described below, the wireless communication terminal 201 canconfirm that the wireless communication base station 101 accepts thesupported notification on the frequency channel ch.2.

(Effect)

Although the wireless communication base station does not make theannouncement and notification of the information about another frequencychannel, the wireless communication terminal which is supported with theplural frequency channels notifies the wireless communication basestation which can simultaneously send and receive on the pluralfrequency channels of the information about another frequency channelwith which the wireless communication terminal is compatible, and thewireless communication base station commonly manages the informationacross the plural frequency channels. Therefore, the connection can bemaintained even if the wireless communication terminal is transferred toanother frequency channel.

Eighteenth Embodiment

In an eighteenth embodiment, the description will be made centering onan aspect added to the sixteenth and seventeenth embodiments. In theeighteenth embodiment, the following point is added to the sixteenth andseventeenth embodiments. That is, in the case where the wirelesscommunication terminal changes the frequency channel to establish theconnection with the wireless communication base station again, theinformation on the wireless communication terminal is utilized when theinformation on the wireless communication terminal remains in theconnection management table.

In the configuration of FIG. 6, in the case where the wirelesscommunication terminal 201 changes the frequency channel ch.1 to thefrequency channel ch.2 to establish the connection with the wirelesscommunication base station 101 without making the request to change thefrequency channel ch.1 to the frequency channel ch.2 to the wirelesscommunication base station 101, when the information about the frequencychannel ch.2 of the wireless communication terminal 201 is retained inthe connection management table of the wireless communication basestation 101, the wireless communication base station 101 notifies thewireless communication terminal 201 that the wireless communication basestation 101 has the information about the frequency channel ch.2 of thewireless communication terminal 201 at the stage in which the wirelesscommunication terminal 201 is transferred to the frequency channel ch.2to try the connection with the wireless communication base station 101.For example, the wireless communication terminal 201 performs thescanning on the frequency channel ch.2 again, adjusts a timer of itselfto a timer of the wireless communication base station 101 based on timerinformation (in the IEEE 802.11 wireless LAN standard, a item calledtime stamp is used) in the beacon frame or probe response frame sent bythe wireless communication base station 101 (in the IEEE 802.11 wirelessLAN standard, join operation), and is reconnected to the wirelesscommunication base station 101 on the frequency channel ch.2 through theauthentication process and the association process. The wirelesscommunication base station 101 understands that the wirelesscommunication terminal 201 is being connected to the wirelesscommunication base station 101 in receiving the probe request framethrough the scanning process or in the authentication process, andnotifies the wireless communication terminal 201 that the wirelesscommunication base station 101 retains the information on thecommunication system with which the wireless communication terminal 201is supported on the frequency channel ch.2. The notification that theinformation is retained may be made using the probe response frame or amanagement frame called subtype 7. Therefore, the wireless communicationterminal 201 recognizes that the wireless communication base station 101already has the information on the communication system with which thewireless communication terminal 201 is supported on the frequencychannel ch.2, so that a simple association process can be realized whilethe supported communication system on the frequency channel ch.2 isomitted. Such a simple process may not be performed using theassociation request frame and the association response frame, and mayinstead be performed while a management frame called a management framecalled subtype 8 and a management frame subtype 9 which is the responseframe of the subtype 8 are provided. Similarly to the ninth embodiment,the encryption system which is already set on the frequency channel ch.1is also used on the frequency channel ch.2, whereby the setting of theencryption system may be omitted on the frequency channel ch.2.

(Effect)

When the wireless communication base station retains the information onthe plural supported frequency channels of the wireless communicationterminal, even if the wireless communication terminal does notpreviously notify the wireless communication base station that thewireless communication terminal is transferred among the pluralfrequency channels with which the wireless communication base station iscompatible, the wireless communication base station can conduct thecommunication with the wireless communication terminal using theinformation which is already retained in establishing the connectionwith the wireless communication terminal on another supported frequencychannel, and the connection setting can be simplified on the transferredfrequency channel.

Nineteenth Embodiment

In a nineteenth embodiment, the description will be made centered on anaspect differing with the first to thirteenth embodiments. Thenineteenth embodiment differs from the first to thirteenth embodimentsin that the announcement and notification of the communication systemwith which the wireless communication base station and the wirelesscommunication terminal are supported are made by the PHY system.

In the configuration of FIG. 6, it is assumed that the wirelesscommunication base station 101 and the wireless communication terminals201 and 202 are operated pursuant to the IEEE 802.11 wireless LANstandard. For example, OFDM (Orthogonal Frequency Division Multiplexing)is used in IEEE 802.11a, DSSS (Direct Sequence Spread Spectrum) and CCK(Complementary Code Keying) are used in IEEE 802.11b, and OFDM (calledERP-OFDM in IEEE 802.11g, ERP is an abbreviated form of Extended RatePHY conforming to Clause 19, that is, an extended rate of the PHY layerpursuant to the clause 19 of the IEEE 802.11 standard) and an ERP-PBCC(Packet Binary Convolutional Code) mode and a DSSS-OFDM mode as optionsare used in IEEE 802.11g. In the nineteenth embodiment, the announcementand notification are made using the above-described systems. Forexample, the announcement and notification are made using OFDM insteadof IEEE 802.11a, and using DSSS instead of IEEE 802.11b. It may beassumed that the nineteenth embodiment is used based on the IEEE 802.11wireless LAN standard. Alternatively, the wireless communicationterminal (including the wireless communication base station) may benotified of the IEEE 802.11 wireless LAN by a MAC frame format of IEEE802.11 at a necessary or common PHY rate, or may implicitly be notifiedfrom the MAC frame format of IEEE 802.11 at the necessary or common PHYrate.

The wireless communication base station or wireless communicationterminal which receives the announcement and notification by the PHYsystem can recognize the communication standard from the frequencychannel included in contents of the announcement and notification. Forexample, when the wireless communication base station 101 notifies thewireless communication terminal 201 that another supported frequencychannel is 2.4 GHz bandwidth in the beacon frame sent in the 5 GHzbandwidth and OFDM is the supported PHY system, the wirelesscommunication terminal 201 located in the 5 GHz bandwidth can recognizethat the use of OFDM in the 2.4 GHz bandwidth is supported with ERP-OFDMof IEEE 802.11g. Similarly, when the wireless communication terminal 201notifies the wireless communication base station 101 of the supportedinformation about another frequency channel using the associationrequest frame, the wireless communication base station 101 can recognizethe information.

(Effect)

The announcement and notification are made by the PHY system, so thatthe information similar to that of the communication standard system canbe imparted from the information about the frequency channelcorresponding to the PHY system which can be utilized across the pluralfrequency channels.

[Additional Statement]

(1) In accordance with a first aspect of the embodiments, a wirelesscommunication base station which can simultaneously conductcommunication on at least two frequency channels is characterized inthat a notification of an identifier of a second frequency channel and acommunication system is made on a first frequency channel, the secondfrequency channel being in a wireless packet receivable state except forthe first frequency channel, the communication system being used on thesecond frequency channel, a communication system is retained in aconnection management table along with an identifier of a wirelesscommunication terminal and an identifier of a frequency channel, thecommunication system being able to be used by the wireless communicationterminal, the wireless communication terminal making a notification ofthe communication system when connection of the wireless communicationterminal is permitted on the first frequency channel, and thecommunication is conducted with the wireless communication terminal onthe second frequency channel using the communication system when arequest from the wireless communication terminal to change the firstfrequency channel to the second frequency channel is permitted, thecommunication system being able to be used by the wireless communicationterminal on the connection management table from the identifier of thewireless communication terminal in the communication systems used on thesecond frequency channel.

(Effect of Additional Statement (1))

The notification of the communication system used on the secondfrequency channel is made on the first frequency channel, so that thewireless communication terminal which performs the transmission andreception on the first frequency channel can recognize the communicationsystem which is used on the second frequency channel by the wirelesscommunication base station. Additionally, the communication system whichcan be used by the wireless communication terminal whose connection ispermitted is retained along with the identifier of the wirelesscommunication terminal and the identifier of the frequency channel, sothat the wireless communication terminal can be moved between thefrequency channels supported by the wireless communication base stationwithout tentatively terminating the connection with the wirelesscommunication terminal.

(1-1) In accordance with a second aspect of the embodiments, a wirelesscommunication base station which can simultaneously conductcommunication on at least two frequency channels is characterized inthat a notification of an identifier of a second frequency channel and acommunication system is made on a first frequency channel, the secondfrequency channel being in a wireless packet receivable state except forthe first frequency channel, the communication system being used on thesecond frequency channel, a communication system is retained in aconnection management table along with an identifier of a wirelesscommunication terminal and an identifier of a frequency channel, thecommunication system being able to be used on the first frequencychannel by the wireless communication terminal, the wirelesscommunication terminal making a notification of the communication systemwhen connection of the wireless communication terminal is permitted onthe first frequency channel, pieces of information on the identifier ofthe second frequency channel and the communication system which can beused on the second frequency channel of the wireless communicationterminal are added to the connection management table while correlatedwith the identifier of the wireless communication terminal when anotification of the communication system which can be used on the secondfrequency channel is received from the wireless communication terminal,and the communication is conducted with the wireless communicationterminal on the second frequency channel using the communication systemwhen a request from the wireless communication terminal to change thefirst frequency channel to the second frequency channel is permitted,the communication system being able to be used by the wirelesscommunication terminal on the connection management table from theidentifier of the wireless communication terminal in the communicationsystems used on the second frequency channel.

(Effect of Additional Statement (1-1))

The notification of the communication system which can be used on thesecond frequency channel is additionally made on the first frequencychannel after the connection. Therefore, the effects similar to those ofthe first aspect of the embodiments can be obtained, that is, a delaycan be granted in order to prepare a notification frame relating to thecommunication system which can be used on the second frequency channelby the wireless communication terminal, and the communication cancontinuously be conducted with no re-setting after the channel changewhile a load is reduced during a connection setting.

(1-2) In accordance with a third aspect of the embodiments, a wirelesscommunication base station is the wireless communication base stationdescribed in the additional statement (1) or (1-1), and is characterizedin that the wireless communication base station updates the informationon the supported connection management table when receiving arenotification of the usable communication system or a renotification ofthe usable frequency channel and the usable communication system fromthe wireless communication terminal whose connection is permitted.

(Effect of Additional Statement (1-2))

The information on the connection management table is updated byreceiving the renotification of the usable communication system from thewireless communication terminal, so that the communication can beconducted by the appropriate communication system which is supportedwith the communication state of the wireless communication terminal.

(1-3-1) In accordance with a fourth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (1), (1-1), or (1-2), andis characterized in that the communication system is expressed by thetype of communication standard.

(Effect of Additional Statement (1-3-1))

The notification of the type of the communication standard used on thesecond frequency channel is made on the first frequency channel, so thatthe wireless terminal which performs the transmission and reception onthe first frequency channel can recognize the type of the communicationstandard which is used on the second frequency channel by the wirelesscommunication base station. Additionally, the type of the communicationstandard which can be used by the wireless communication terminal whoseconnection is permitted is retained along with the identifier of thewireless communication terminal and the identifier of the frequencychannel, so that the wireless communication terminal can be movedbetween the frequency channels supported by the wireless communicationbase station without tentatively terminating the connection with thewireless communication terminal.

(1-3-2) In accordance with a fifth aspect of the embodiments, a wirelesscommunication base station is the wireless communication base stationdescribed in the additional statement (1-3-1), and is characterized inthat extended systems in the same communication standard aredistinguished from each other in the type of the communication standard.

(Effect of Additional Statement (1-3-2))

The notification of the type of the extended system in the samecommunication standard used on the second frequency channel is made onthe first frequency channel, so that the wireless terminal whichperforms the transmission and reception on the first frequency channelcan recognize the type of the extended system in the same communicationstandard which is used on the second frequency channel by the wirelesscommunication base station. Additionally, the type of the extendedsystem in the same communication standard which can be used by thewireless communication terminal whose connection is permitted isretained along with the identifier of the wireless communicationterminal and the identifier of the frequency channel, so that thewireless communication terminal can be moved between the frequencychannels supported by the wireless communication base station withouttentatively terminating the connection with the wireless communicationterminal.

(2) In accordance with a sixth aspect of the embodiments, a wirelesscommunication base station which can simultaneously conductcommunication on at least two frequency channels is characterized inthat plural modulation and coding schemes are used in the frequencychannels, a notification of an identifier of a second frequency channeland a modulation and coding scheme is made on a first frequency channel,the second frequency channel being in a wireless packet receivable stateexcept for the first frequency channel, the modulation and coding schemebeing used on the second frequency channel, a modulation and codingscheme is retained in the connection management table along with theidentifier of the wireless communication terminal and the identifier ofthe frequency channel, the modulation and coding scheme being able to beused by the wireless communication terminal, the wireless communicationterminal making a notification of the modulation and coding scheme whenthe connection request from the wireless communication terminal isreceived and permitted on the first frequency channel, a determinationas to whether or not the modulation and coding scheme which can be usedby the wireless communication terminal on the connection managementtable can be used on the second frequency channel is made from theidentifier of the wireless communication terminal when receiving therequest to change the first frequency channel to the second frequencychannel from the wireless communication terminal, the identifier of thefrequency channel is updated to the identifier of the second frequencychannel to retain the updated identifier of the second frequency channelwhen the determination that the modulation and coding scheme can be usedon the second frequency channel is made to permit the use of themodulation and coding scheme, and the communication is conducted withthe wireless communication terminal on the second frequency channelusing the modulation and coding scheme, the modulation and coding schemebeing able to be used by the wireless communication terminal on theconnection management table from the identifier of the wirelesscommunication terminal in the modulation and coding schemes used on thesecond frequency channel.

(Effect of Additional Statement (2))

The notification of the modulation coding communication system of thesecond frequency channel is made on the first frequency channel of thetwo frequency channels in which plural modulation and coding schemes areused, so that the wireless communication terminal which performs thetransmission and reception on the first frequency channel can recognizethe modulation and coding scheme which is used on the second frequencychannel by the wireless communication base station. Additionally, themodulation and coding scheme which can be used by the wirelesscommunication terminal whose connection is permitted is retained alongwith the identifier of the wireless communication terminal and theidentifier of the frequency channel. Therefore, the determination as towhether or not the modulation and coding scheme which can be used by thewireless communication terminal can be used on the second frequencychannel can be made when the request to change the first frequencychannel to the second frequency channel is received from the wirelesscommunication terminal, and the communication with the wirelesscommunication terminal can be assured on the second frequency channelwhen the determination that the modulation and coding scheme can be usedon the second frequency channel is made to permit the use of themodulation and coding scheme. On such basis, the wireless communicationterminal can be moved between the frequency channels supported by thewireless communication base station without tentatively terminating theconnection with wireless communication terminal.

(2-1) In accordance with a seventh aspect of the embodiments, a wirelesscommunication base station which can simultaneously conductcommunication on at least two frequency channels is characterized inthat plural modulation and coding schemes are used in the frequencychannels, a notification of an identifier of a second frequency channeland a modulation and coding scheme is made on a first frequency channel,the second frequency channel being in a wireless packet receivable stateexcept for the first frequency channel, the modulation and coding schemebeing used on the second frequency channel, a modulation and codingscheme is retained in the connection management table along with theidentifier of the wireless communication terminal and the identifier ofthe frequency channel, the modulation and coding scheme being able to beused by the wireless communication terminal on the first frequencychannel, the wireless communication terminal making a notification ofthe modulation and coding scheme when the connection request from thewireless communication terminal is received and permitted on the firstfrequency channel, pieces of information on the identifier of the secondfrequency channel and the modulation and coding scheme which can be usedon the second frequency channel of the wireless communication terminalare added to the connection management table while correlated with theidentifier of the wireless communication terminal when a notification ofthe modulation and coding scheme which can be used on the secondfrequency channel is received from the wireless communication terminal,a determination as to whether or not the modulation and coding schemewhich can be used by the wireless communication terminal on theconnection management table can be used on the second frequency channelis made from the identifier of the wireless communication terminal whena request to change the first frequency channel to the second frequencychannel is received from the wireless communication terminal, and thecommunication is conducted with the wireless communication terminal onthe second frequency channel using the modulation and coding scheme whenthe determination that the modulation and coding scheme can be used onthe second frequency channel is made to permit the use of the modulationand coding scheme, the modulation and coding scheme being able to beused by the wireless communication terminal on the connection managementtable from the identifier of the wireless communication terminal in themodulation and coding schemes used on the second frequency channel.

(Effect of Additional Statement (2-1))

The notification of the modulation and coding scheme which can be usedon the second frequency channel is additionally made on the firstfrequency channel after the setting. Therefore, the effects similar tothose of the sixth aspect of the embodiments can be obtained, that is, adelay can be granted in order to prepare a notification frame relatingto the modulation and coding scheme which can be used on the secondfrequency channel by the wireless communication terminal, and thecommunication can continuously be conducted with no re-setting after thechannel change while a load is reduced during a connection setting.

(2-2) In accordance with an eighth aspect of the embodiments, a wirelesscommunication base station is the wireless communication base stationdescribed in the additional statement (2) or (2-1), and is characterizedin that the wireless communication base station updates the informationon the supported connection management table when receiving arenotification of the usable modulation and coding scheme or arenotification of the usable frequency channel and the usable modulationand coding scheme from the wireless communication terminal whoseconnection is permitted.

(Effect of Additional Statement (2-2))

The information on the connection management table is updated byreceiving the renotification of the usable modulation and coding schemefrom the wireless communication terminal, so that the communication canbe conducted by the appropriate modulation and coding scheme which issupported with the communication state of the wireless communicationterminal.

(3-1) In accordance with a ninth aspect of the embodiments, a wirelesscommunication base station is the wireless communication base stationdescribed in the additional statement (1), (1-1), (2), or (2-1), and ischaracterized in that a notification of the communication system ormodulation and coding scheme used on the second frequency channel ismade on the second frequency channel.

(Effect of Additional Statement (3-1))

The notification of the communication system or modulation and codingscheme used on the second frequency channel is made on the secondfrequency channel, so that other wireless communication base stations orwireless communication terminals which are receivable on the secondfrequency channel can recognize what communication system or modulationand coding scheme is used on the second frequency channel by thewireless communication base station. In other wireless communicationbase stations or wireless communication terminals, aninterference-prevention measure can be taken by the recognition. In thewireless communication terminal, the wireless communication base stationcan be specified as a connected candidate of a wireless communicationbase station by such recognition.

(3-2) In accordance with a tenth aspect of the embodiments, a wirelesscommunication base station is the wireless communication base stationdescribed in the additional statement (1), (1-1), (2), or (2-1), and ischaracterized in that a notification that the wireless communicationbase station has the same first frequency channel is made on the secondfrequency channel.

(Effect of Additional Statement (3-2))

The notification of the identifier of the wireless communication basestation is made on the second frequency channel, so that thenotification that the same wireless communication base station isoperated on the first and second frequency channels is made on thesecond frequency channel. In other wireless communication base stationsor wireless communication terminals, an interference-prevention measurecan be taken by such recognition. The wireless communication terminalcan recognize the wireless communication base station to send thewireless packet. Additionally, the wireless communication terminalconducts the communication with the wireless communication base stationon the first frequency channel, changes the first frequency channel tothe second frequency channel, and conducts the communication again withthe wireless communication base station.

(3-2-1-1) In accordance with an eleventh aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (3-2), and ischaracterized in that a wireless packet is sent on all wireless packetsendable and receivable frequency channels, the wireless packet beingaddressed to all or a part of plural wireless communication terminals,the wireless communication terminals being connected on one of frequencychannels in wireless packet sendable and receivable states.

(Effect of Additional Statement (3-2-1-1))

The wireless packet addressed to the plural wireless communicationterminals is sent on all the wireless packet sendable and receivablefrequency channels, so that the destination wireless communicationterminal that can move the frequency channel can securely receive thewireless packet. Additionally, it is not necessary that the wirelesscommunication base station correctly specify the connected frequencychannel including the movement of the frequency channel to connectwireless communication terminal in transmitting the wireless packet, sothat the load on processing can be reduced.

(3-2-1-2) In accordance with a twelfth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (3-2-1-1), and ischaracterized in that an identical value is inserted in a itemindicating order of a delivery number when the wireless packet addressedto all or a part of plural wireless communication terminals is sent onall the wireless packet sendable and receivable frequency channels.

(Effect of Additional Statement (3-2-1-2))

The identical value is inserted in the item indicating the order of thedelivery number when the wireless packet addressed to the same pluralwireless communication terminals is sent on the plural frequencychannels. Therefore, when the transmission timing is shifted between theplural frequency channels, the wireless communication terminal which ismoved between the frequency channels during the shift of thetransmission timing or the wireless communication terminal which isreceivable on the plural frequency channels can recognize that thereceived packets are overlapping even if the wireless communicationterminal receives the same packets on the plural frequency channels.

(3-2-2-1) In accordance with a thirteenth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (3-2), and ischaracterized in that a first item and a second item are provided in thewireless packet used in the notification, the first item indicating theidentifier of the wireless communication base station which can be alsoused in a wireless communication base station which can conductcommunication only on the single frequency channel, the identifierinserted in the first item differs from channel to channel, and theidentifier indicating the same wireless communication base stationbetween the frequency channels is inserted in the second field.

(Effect of Additional Statement (3-2-2-1))

The notification of the same wireless communication base station as thefirst frequency channel is made by the item different from the itemindicating the identifier of the wireless communication base stationwhich can be used in a wireless communication base station which canconduct the communication only on the single frequency channel.Therefore, when the notification is received by the wirelesscommunication terminal which can be connected only to the wirelesscommunication base station which can conduct the communication only onthe single frequency channel, the wireless communication base stationwhich can conduct the communication only on the single frequency channelcan be recognized as another wireless communication base station toconnect the wireless communication terminal to the wirelesscommunication base station. In the wireless communication terminal whichcan be connected to the wireless communication base station which canconduct the communication on the plural frequency channels, the wirelesscommunication terminal can recognize the wireless communication basestation which can conduct the communication on the plural frequencychannels as the same wireless communication base station to connect thewireless communication terminal to the wireless communication basestation.

(4) In accordance with a fourteenth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (1), (1-1), (2), or (2-1),and the wireless communication base station is characterized in that thenotification of the communication system or modulation and coding schemeused in the first frequency channel is made on the first frequencychannel.

(Effect of Additional Statement (4))

The notification of the communication system or modulation and codingscheme used in the first frequency channel is made on the firstfrequency channel. Therefore, other wireless packet receivable wirelesscommunication base stations or wireless communication terminals canrecognize on the first frequency channel that the wireless communicationbase station is operated on the first and second frequency channels andwhich communication system or modulation and coding scheme is used onthe first frequency channel. In other wireless communication basestations or wireless communication terminals, an interference-preventionmeasure can be taken by such recognition. In the wireless communicationterminal, the wireless communication base station can be specified as acandidate of a connected wireless communication base station by suchrecognition.

(5) In accordance with a fifteenth aspect of the embodiments, a wirelesscommunication base station is the wireless communication base stationdescribed in the additional statement (1), (1-1), (2), or (2-1), and ischaracterized in that the identifier of the wireless communicationterminal is a management number allocated to the wireless communicationterminal when the wireless communication base station permits thewireless communication terminal to be connected thereto.

(Effect of Additional Statement (5))

The management number allocated to the wireless communication terminalwhen the wireless communication base station permits the wirelesscommunication terminal to be connected thereto is retained as theidentifier of the wireless communication terminal by the connectionmanagement table, so that the wireless communication base station canidentify the wireless communication terminal using the uniqueidentifier, and the management of the wireless communication terminalcan be simplified.

(6) In accordance with a sixteenth aspect of the embodiments, a wirelesscommunication base station is the wireless communication base stationdescribed in the additional statement (1), (1-1), (2), or (2-1), and ischaracterized by including a queue in which the sent wireless packet isstored in each frequency channel, and the wireless packet addressed tothe wireless communication terminal is moved from a first queue for thefirst frequency channel to a second queue for the second frequencychannel when the request from the wireless communication terminal tochange the first frequency channel to the second frequency channel ispermitted.

(Effect of Additional Statement (6))

The wireless communication base station includes the queue in which thesent wireless packet is stored in each frequency channel, and thewireless packet addressed to the wireless communication terminal ismoved to the transmission queue of the supported frequency channel inresponse to the frequency channel change request from the wirelesscommunication terminal. Therefore, the wireless communication terminalmoved between the frequency channels can send the wireless packetaddressed to the wireless communication terminal on the frequencychannel on which the communication is conducted.

(7) In accordance with a seventeenth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (1), (1-1), (2), or (2-1),and is characterized in that, when the request from the wirelesscommunication terminal to change the first frequency channel to thesecond frequency channel is permitted, the wireless communication basestation starts the communication with the wireless communicationterminal on the second frequency channel after at least a fixed timeelapses since the permission.

(Effect of Additional Statement (7))

The wireless communication base station starts the communication withthe wireless communication terminal on the changed frequency channelafter at least the fixed time elapses since the request from thewireless communication terminal to change the first frequency channel tothe second frequency channel is permitted. Therefore, a delay can begranted in order to prepare the start of the communication between thewireless communication base station and the wireless communicationterminal on the changed frequency channel.

(7-1) In accordance with an eighteenth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (7), and is characterizedin that at least a time necessary to move the frequency channel of thewireless communication terminal is set at the fixed time.

(Effect of Additional Statement (7-1))

The communication is started between the wireless communication basestation and the wireless communication terminal on the changed frequencychannel after at least the time necessary to move the frequency channelof the wireless communication terminal elapses. Therefore, that thewireless communication terminal is in the receivable state on thechanged frequency channel can be assured to start the transmission ofthe wireless packet.

(7-1-1) In accordance with a nineteenth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (7-1), and ischaracterized in that a time necessary to change the frequency channelis obtained from the wireless communication terminal before the requestto change the first frequency channel to the second frequency channel ispermitted.

(Effect of Additional Statement (7-1-1))

The time necessary to change the frequency channel is obtained from thewireless communication terminal before the request to change the firstfrequency channel to the second frequency channel is permitted, and thetime necessary to move the frequency channel of the wirelesscommunication terminal is correctly recognized. Then the communicationis started between the wireless communication base station and thewireless communication terminal on the changed frequency channel afterat least the time elapses, so that the degree of certainty can beenhanced for the assurance that the wireless communication terminal isin the receivable state on the changed frequency channel.

(7-2) In accordance with a twentieth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (6), and is characterizedin that, when the request from the wireless communication terminal tochange the first frequency channel to the second frequency channel ispermitted, the wireless communication base station starts thecommunication with the wireless communication terminal on the secondfrequency channel after at least the time necessary to move the wirelesspacket from the first queue to the second queue elapses since thepermission.

(Effect of Additional Statement (7-2))

The wireless communication base station starts the communication withthe wireless communication terminal on the changed frequency channelafter at least the time necessary to move the wireless packet addressedto the wireless communication terminal between the queues elapses, sothat the wireless packet addressed to the wireless communicationterminal can surely be sent to the wireless communication terminal onthe changed frequency channel.

(7-3) In accordance with a twenty-first aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (7), and is characterizedin that a determination of the fixed time is made by exchange of thewireless packet with the wireless communication terminal before thechange to the second frequency channel is permitted.

(Effect of Additional Statement (7-3))

The time to start the communication with the wireless communicationterminal on the changed frequency channel is determined by the exchangeof the wireless packet, so that the start of the communication can beassured after the communication can surely be conducted between thewireless communication base station and the wireless communicationterminal on the changed frequency channel.

(8) In accordance with a twenty-second aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (1), (1-1), (2), or (2-1),and is characterized in that a notification of a usage rate of thesecond frequency channel is made on the first frequency channel.

(Effect of Additional Statement (8))

The information for making a determination of the transition to anotherfrequency channel can be provided to the wireless communication terminalby making the notification of the usage rate of another frequencychannel.

(9) In accordance with a twenty-third aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (1), (1-1), (2), or (2-1),and is characterized in that a notification of a second bandwidth whichis the bandwidth of the second frequency channel is made on the firstfrequency channel.

(Effect of Additional Statement (9))

The notification of the bandwidth of another frequency channel is made,so that the wireless communication terminal determines whether or notthe wireless communication terminal can conduct the communication withthe bandwidth of another frequency channel.

(10) In accordance with a twenty-fourth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (1), (1-1), (2), or (2-1),and is characterized in that security information set in conducting thecommunication with the wireless communication terminal on the firstfrequency channel is retained in the connection management table whilecorrelated with the identifier of the wireless communication terminal,and the communication is conducted with the wireless communicationterminal on the second frequency channel using the retained securityinformation when the request from the wireless communication terminal tochange the first frequency channel to the second frequency channel ispermitted.

(Effect of Additional Statement (10))

The security information is managed along with the identifier of thewireless communication terminal, and the same security information isused on the changed frequency channel when the request of the change toanother frequency channel is permitted, so that the communication can bestarted unless the security setting is performed again on the changedfrequency channel.

(10-1) In accordance with a twenty-fifth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (10), and is characterizedin that a security system which can be used by the wirelesscommunication terminal is retained in the connection management tablewhile correlated with the identifier of the wireless communicationterminal, the notification of the security system being made on thefirst frequency channel by the wireless communication terminal, whetheror not the security system is matched with a security system necessaryfor the wireless communication base station on the second frequencychannel is referred to from the connection management table when thewireless communication terminal makes the request to change the firstfrequency channel to the second frequency channel, and the reference isused to make the determination of the permission.

(Effect of Additional Statement (10-1))

The security system which can be used by the wireless communicationterminal is recognized before the request of the change to anotherfrequency channel, and the security system is used to determine whetheror not the request of the change to another frequency channel ispermitted, so that the security can be retained on another frequencychannel. Additionally, when the security system necessary for thewireless communication base station is not satisfied, the connectionrequest from the wireless communication terminal which is known to berejected on another frequency channel is previously recognized by thewireless communication terminal, so that the occupancy of the frequencychannel caused by the exchange of the wireless packet due to the wastedconnection can be reduced. When the change of the wireless communicationterminal to another frequency channel is permitted, the information onthe security system of which the wireless communication terminalnotifies the wireless communication base station can be used in thecommunication with the wireless communication terminal on the changedfrequency channel.

(10-1-1) In accordance with a twenty-sixth aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (10-1), and ischaracterized in that, in the permission of the request of the change tosecond frequency channel, the communication is conducted with thewireless communication terminal on the second frequency channel usinginformation on a retained security setting when a first security systemused on the first frequency channel can be used on the second frequencychannel, one of the corresponding security systems which are supportedwith the second frequency channel of the wireless communication basestation in the security systems which can be used on the secondfrequency channel by the wireless communication terminal is selected asa second security system from the connection management table when thefirst security system cannot be used on the second frequency channel,and the second security system is set before the communication isconducted with the wireless communication terminal on the secondfrequency channel using such security system.

(Effect of Additional Statement (10-1-1))

When the security system before the frequency channel change can be usedas the frequency channel after the frequency channel change, thecommunication is conducted using the same security information, so thatthe re-setting of the exchange of the wireless packet can be omitted.The exchange of the wireless packet is re-set in order to use thesecurity system on the changed frequency channel. When the securitysystems supported with the wireless communication terminal exist in thesecurity systems necessary for the wireless communication base stationalthough the security system before the frequency channel change cannotbe used on the changed frequency channel, the setting of one of thesecurity systems which are supported with the wireless communicationterminal is performed on the changed frequency channel between thewireless communication base station and the wireless communicationterminal, so that the security necessary for the wireless communicationbase station on the changed frequency channel can be retained.

(10-2) In accordance with a twenty-seventh aspect of the embodiments, awireless communication base station is the wireless communication basestation described in the additional statement (10-1), and ischaracterized in that a notification of the security system necessaryfor the second frequency channel is made on the first frequency channel.

(Effect of Additional Statement (10-2))

The notification of the security level necessary for another frequencychannel is made. Therefore, a security level necessary for anotherfrequency channel can be changed, and the wireless communicationterminal can determine whether or not another frequency channel issupported with the security system of the wireless communicationterminal.

(11) In accordance with a twenty-eighth aspect of the embodiments, awireless communication terminal which can conduct communication on atleast two frequency channels, selecting at least one of the frequencychannels to conduct the communication, is characterized in that thewireless communication base station which can simultaneously conduct thecommunication on the first and second frequency channels is notified onthe first frequency channel of communication systems which can be usedon the first and second frequency channels of the wireless communicationterminal, the communication is conducted with the wireless communicationbase station on the first frequency channel when connection is permittedby the wireless communication base station, and the communication isconducted with wireless communication base station on the secondfrequency channel when the change to the second frequency channel ispermitted by the wireless communication base station.

(Effect of Additional Statement (11))

The notification of the communication system which can be used on thesecond frequency channel is made on the first frequency channel, so thatthe wireless communication base station connected on the first frequencychannel can previously recognize the communication system which can beused on the second frequency channel of the wireless communicationterminal and the communication can be started without making thenotification of the connection information necessary for thecommunication on the second frequency channel.

(11-1) In accordance with a twenty-ninth aspect of the embodiments, awireless communication terminal which can conduct communication on atleast two frequency channels, selecting at least one of the frequencychannels to conduct the communication, is characterized in that thewireless communication base station which can simultaneously conduct thecommunication on the first and second frequency channels is notified onthe first frequency channel of communication systems which can be usedon the first frequency channel of the wireless communication terminal,the communication is conducted with the wireless communication basestation on the first frequency channel and a notification of thecommunication system which can be used on the second frequency channelis made during the communication when the connection is permitted by thewireless communication base station, and the communication is conductedwith the wireless communication base station on the second frequencychannel when the change to the second frequency channel is permitted bythe wireless communication base station.

(Effect of Additional Statement (11-1))

Therefore, the effects similar to those of the above-described aspect ofthe embodiments can be obtained, that is, the notification of thecommunication system which can be used on the second frequency channelis additionally made on the first frequency channel after theconnection, so that the delay can be granted in order to prepare anotification frame relating to the communication system which can beused on the second frequency channel by the wireless communicationterminal, and the communication can continuously be conducted with nore-setting after the channel change while the load is reduced during theconnection setting.

(11-2) In accordance with a thirtieth aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (11) or (11-1), and ischaracterized in that, when the usable communication system is changed,the wireless communication base station which permits the connection isnotified again of the usable communication system, or of the usablefrequency channel and the usable communication system.

(Effect of Additional Statement (11-2))

The wireless communication base station is notified again of theinformation when the usable communication system is changed, so that thecommunication can be conducted by the appropriate communication systemwhich is supported with the communication state of the wirelesscommunication terminal.

(11-3-1) In accordance with a thirty-first aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (11) or (11-1), and ischaracterized in that the communication system is expressed by the typeof communication standard.

(Effect of Additional Statement (11-3-1))

The notification of the type of the communication standard which can beused on the second frequency channel is made on the first frequencychannel. Therefore, the wireless communication base station which is thedestination connected on the first frequency channel can previouslyrecognize the type of the communication standard which can be used onthe second frequency channel of the wireless communication terminal, andthe communication can be started without making the renotification ofthe connection information necessary for the communication on the secondfrequency channel.

(11-3-2) In accordance with a thirty-second aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (11-3-1), and is characterized inthat, in the type of the communication standard, extended systems in thesame communication standard are distinguished from each other.

(Effect of Additional Statement (11-3-2))

The notification of the type of the extended systems in the samecommunication standard which can be used on the second frequency channelis made on the first frequency channel. Therefore, the wirelesscommunication base station which is the destination connected on thefirst frequency channel can previously recognize the type of theextended systems in the same communication standard which can be used onthe second frequency channel of the wireless communication terminal, andthe communication can be started without making the renotification ofthe connection information necessary for the communication on the secondfrequency channel.

(12) In accordance with a thirty-third aspect of the embodiments, awireless communication terminal which can conduct communication on atleast two frequency channels using plural modulation and coding schemes,selecting at least one of the frequency channels to conduct thecommunication, is characterized in that, when a connection request issent on the first frequency channel to the wireless communication basestation which can simultaneously conduct communication on the first andsecond frequency channels using the plural modulation and codingschemes, a notification of at least a modulation and coding scheme whichcan be used by the wireless communication terminal in modulation andcoding schemes on the second frequency channel is made in addition tothe modulation and coding scheme which can be used on the firstfrequency channel of the wireless communication terminal, thenotifications of the modulation and coding schemes on the firstfrequency channel being made by the wireless communication base station,the communication is conducted with the wireless communication basestation on the first frequency channel using the notified modulation andcoding scheme which can be used by the wireless communication terminalon the first frequency channel when the connection is permitted by aresponse from the wireless communication base station, a request ofchange to the second frequency channel is made to the wirelesscommunication base station, and the communication is conducted with thewireless communication base station on the second frequency channelusing the notified modulation and coding scheme which can be used on thesecond frequency channel by the wireless communication terminal when thechange to the second frequency channel is permitted by the response fromthe wireless communication base station.

(Effect of Additional Statement (12))

The notification of the modulation and coding scheme which can be usedon the second frequency channel of the two frequency channels using theplural modulation and coding schemes is made on the first frequencychannel in the connection, so that the wireless communication basestation which can simultaneously conduct the communication on the firstand second frequency channels can recognize the modulation and codingscheme which can be used on the second frequency channel of the wirelesscommunication terminal through the first frequency channel and thecommunication can be started without making the notification of theconnection information necessary for the communication on the secondfrequency channel. In the connection and in the channel change, therequest is sent from the wireless communication terminal, and theresponse is received from the wireless communication base station.Therefore, consistency of the connection information can be assuredbetween the wireless communication terminal and the wirelesscommunication base station.

(12-1) In accordance with a thirty-fourth aspect of the embodiments, awireless communication terminal which can conduct communication on atleast two frequency channels using plural modulation and coding schemes,selecting at least one of the frequency channels to conduct thecommunication, is characterized in that the wireless communication basestation which can simultaneously conduct communication on the first andsecond frequency channels using plural modulation and coding schemes isnotified on the first frequency channel of a modulation and codingscheme which can be used on the first frequency channel by the wirelesscommunication terminal, the communication is conducted with the wirelesscommunication base station on the first frequency channel using themodulation and coding scheme which can be used by the wirelesscommunication terminal on the first frequency channel when theconnection is permitted by a response from the wireless communicationbase station, a notification of the modulation and coding scheme whichcan be used on the second frequency channel is made during thecommunication, a request of change to the second frequency channel ismade to the wireless communication base station, and the communicationis conducted with the wireless communication base station on the secondfrequency channel using the notified modulation and coding scheme whichcan be used on the second frequency channel by the wirelesscommunication terminal when the change to the second frequency channelis permitted by the response from the wireless communication basestation.

(Effect of Additional Statement (12-1))

Therefore, the effects similar to those of the above-described aspect ofthe embodiments can be obtained, that is, the notification of themodulation and coding scheme which can be used on the second frequencychannel is additionally made on the first frequency channel after theconnection, so that the delay can be granted in order to prepare anotification frame relating to the modulation and coding scheme whichcan be used on the second frequency channel by the wirelesscommunication terminal, and the communication can continuously beconducted with no re-setting after the channel change while the load isreduced during the connection setting.

(12-2) In accordance with a thirty-fifth aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (12) or (12-1), and ischaracterized in that, when the usable modulation and coding scheme ischanged, the wireless communication base station whose connection ispermitted is notified again of the usable modulation and coding scheme,or of the usable frequency channel and the usable modulation and codingscheme.

(Effect of Additional Statement (12-2))

When the usable modulation and coding scheme is changed, the wirelesscommunication base station is notified of the information again, so thatthe communication can be conducted by the appropriate modulation andcoding scheme which is supported with the communication state of thewireless communication terminal.

(13) In accordance with a thirty-sixth aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (11), (11-1), (12), or (12-1), andis characterized in that a notification of the communication system ormodulation and coding scheme which can be used on the first frequencychannel is made when the wireless communication terminal is connected onthe first frequency channel to the wireless communication base stationwhich can conduct communication on single frequency channel, thecommunication is conducted with the wireless communication base stationon the first frequency channel when the wireless communication basestation gives the connection permission, the wireless communicationterminal is transferred to the second frequency channel to search forother wireless communication base stations which are operated on thesecond frequency channel in the case of the change to the secondfrequency channel, other wireless communication base stations arenotified of the communication system or modulation and coding schemewhich can be used on the second frequency channel when other connectablewireless communication base stations are detected, and a connectionrequest is made to other wireless communication base stations.

(Effect of Additional Statement (13))

While the wireless communication terminal is connected to the wirelesscommunication base station which can simultaneously conductcommunication on at least two frequency channel, the wirelesscommunication terminal can also be connected to wireless communicationbase stations with which the wireless communication terminal can conductthe communication on the single frequency channel, so that the number ofoptions can be increased in the wireless communication base station withwhich the wireless communication terminal can conduct the communication.A wireless communication base station which can be connected on thesecond frequency channel is searched for when the request to transfer tothe second frequency channel is made even if the wireless communicationterminal is connected to the wireless communication base station withwhich the wireless communication terminal can conduct the communicationon the single frequency channel, the wireless communication base stationis notified of the communication system or modulation and coding schemewhich can be used on the second frequency channel when the connectablewireless communication base station is detected, and the connectionrequest is made to the wireless communication base station. Therefore,the wireless communication terminal can be connected to the wirelesscommunication base station which is operated on the second frequencychannel.

(14) In accordance with a thirty-seventh aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (11), (11-1), (12), or (12-1), andis characterized in that the wireless communication terminal istransferred to the second frequency channel to search other wirelesscommunication base stations which are operated on the second frequencychannel when the permission of the channel change is not given, otherwireless communication base stations are notified of the communicationsystem or modulation and coding scheme which can be used on the secondfrequency channel when other connectable wireless communication basestations are detected, and a connection request is made to otherwireless communication base stations.

(Effect of Additional Statement (14))

While the wireless communication terminal is connected to the wirelesscommunication base station which can simultaneously conductcommunication on at least two frequency channels, other wirelesscommunication base stations which are connectable on the secondfrequency channel are searched for when the permission of the request totransfer to the second frequency channel is not given to the wirelesscommunication base station, other wireless communication base stationsare notified of the communication system or modulation and coding schemewhich can be used on the second frequency channel when other connectablewireless communication base stations are detected, and a connectionrequest is made to other wireless communication base stations.Therefore, the wireless communication terminal can be connected to otherwireless communication base stations which are operated on the secondfrequency channel, and the number of options can be increased in thewireless communication base station with which the wirelesscommunication terminal can conduct the communication.

(15) In accordance with a thirty-eighth aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (11), (11-1, (12), or (12-1), andis characterized in that the wireless communication terminal istransferred to a third frequency channel to search for other wirelesscommunication base stations which are operated on the third frequencychannel when the request to transfer to the third frequency channel ismade, other wireless communication base stations are notified of thecommunication system or modulation and coding scheme which can be usedon the third frequency channel when other connectable wirelesscommunication base stations are detected, and a connection request ismade to other wireless communication base stations.

(Effect of Additional Statement (15))

While the wireless communication terminal is connected to the wirelesscommunication base station which can simultaneously conductcommunication on at least two frequency channels, a wirelesscommunication base station which can be connected on the third frequencychannel is searched for when the request to transfer to the thirdfrequency channel which is not supported with the same wirelesscommunication base station is made, the wireless communication basestation is notified of the communication system or modulation and codingscheme which can be used on the third frequency channel when thewireless communication base station is detected, and the connectionrequest is made to the wireless communication base station. Therefore,the wireless communication terminal can be connected to the wirelesscommunication base station which is operated on the third frequencychannel, and the number of options can be increased in the wirelesscommunication base station with which the wireless communicationterminal can conduct the communication.

(16) In accordance with a thirty-ninth aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (11), (11-1), (12), or (12-1), andis characterized in that, when the wireless communication base stationgives the permission of the request of change to the second frequencychannel, the communication with the wireless communication base stationis started on the second frequency channel after at least a fixed timeelapses since the permission.

(Effect of Additional Statement (16))

The communication is started between the wireless communication basestation and the wireless communication terminal on the changed frequencychannel after at least the fixed time elapses since the wirelesscommunication base station gives the permission of the request of thefrequency channel change, so that the delay can be granted in order toprepare the start of the communication between the wirelesscommunication terminal and wireless communication base station on thechanged frequency channel.

(16-1) In accordance with a fortieth aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (16), and is characterized in thatat least a time necessary to move the frequency channel of the wirelesscommunication terminal is set at the fixed time.

(Effect of Additional Statement (16-1))

The communication is started between the wireless communication basestation and the wireless communication terminal on the changed frequencychannel after at least the time necessary to move the frequency channelof the wireless communication terminal elapses. Therefore, thecommunication can surely be started after the wireless communicationterminal can send and receive on the changed frequency channel.

(16-1-1) In accordance with a forty-first aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (16-1), and is characterized inthat the wireless communication base station is notified of a timenecessary for the frequency channel change before the change to thesecond frequency channel is permitted.

(Effect of Additional Statement (16-1-1))

The wireless communication base station is notified of the timenecessary for the frequency channel change before the change to thesecond frequency channel is permitted, so that the wirelesscommunication base station can correctly recognize the time necessaryfor the frequency channel movement in the wireless communicationterminal and the wireless communication base station can start thetransmission addressed to the wireless communication terminal on thechanged frequency channel after at least the time necessary for thefrequency channel movement elapses.

(16-2) In accordance with a forty-second aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (16), and is characterized in thatthe fixed time is a time which is specified by the wirelesscommunication base station.

(Effect of Additional Statement (16-2))

The communication is started between the wireless communication basestation and the wireless communication terminal on the changed frequencychannel after at least the time specified by the wireless communicationbase station elapses. Therefore, the delay can be granted in order toprepare the start of the communication between the wirelesscommunication terminal and wireless communication base station on thechanged frequency channel, and the communication with the wirelesscommunication base station can surely be started on the changedfrequency channel.

(16-3) In accordance with a forty-third aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (16), and is characterized in thatthe fixed time is determined by the exchange of the wireless packet withthe wireless communication base station before the change to the secondfrequency channel is permitted.

(Effect of Additional Statement (16-3))

The time to start the communication with the wireless communication basestation on the changed frequency channel is determined by the exchangeof the wireless packet, so that the start of the communication can beassured after the communication can surely be conducted between thewireless communication terminal and the wireless communication basestation on the changed frequency channel.

(17) In accordance with a forty-fourth aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (11), (11-1), (12), or (12-1), andis characterized in that a usage rate of the second frequency channel isobtained from the wireless communication base station to determinewhether or not the request to transfer to the second frequency channelis sent.

(Effect of Additional Statement (17))

The usage rate of the second frequency channel is used to determinewhether or not the request to transfer to the second frequency channelis sent, so that the communication can be assured in the case of thetransition to the second frequency channel.

(18) In accordance with a forty-fifth aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (11), (11-1), (12), or (12-1), andis characterized in that a second bandwidth, which is the bandwidth ofthe second frequency channel, is obtained from the wirelesscommunication base station to determine whether or not the request totransfer to the second frequency channel is sent.

(Effect of Additional Statement (18))

The bandwidth of another frequency channel is used to determine whetheror not the request to transfer to the second frequency channel is sent,so that the communication can be assured in the case of the transitionto the second frequency channel.

(19) In accordance with a forty-sixth aspect of the embodiments, awireless communication terminal is the wireless communication terminaldescribed in the additional statement (11), (11-1), (12), or (12-1), andis characterized in that the wireless communication base station isnotified on the first frequency channel of the security system which canbe used on the first and second frequency channels.

(Effect of Additional Statement (19))

The wireless communication base station is notified of the securitysystem which can be used on another frequency channel. Therefore, thewireless communication base station can determine whether or not thepermission is given when the wireless communication terminal makes therequest of the change to another frequency channel, and the informationon the notified security system can be used in the communication withthe wireless communication terminal on the changed frequency channelwhen the permission is given.

(21) In accordance with a forty-seventh aspect of the embodiments, awireless communication system includes a wireless communication basestation which can simultaneously conduct communication on at least twofrequency channels and a wireless communication terminal which cansimultaneously conduct communication on at least two frequency channelsand selecting at least one of the frequency channels to conduct thecommunication, and the wireless communication system is characterized inthat the wireless communication base station notifies the wirelesscommunication terminal of an identifier of a second frequency channeland a communication system on a first frequency channel, the secondfrequency channel being in a wireless packet receivable state except forthe first frequency channel, the communication system being used on thesecond frequency channel, the wireless communication terminal notifiesthe wireless communication base station of communication systems on thefirst frequency channel, the communication systems being able to be usedon the first and second frequency channels of the wireless communicationterminal, the wireless communication base station retains thecommunication system in a connection management table along with anidentifier of the wireless communication terminal and an identifier of afrequency channel, the communication system being able to be used by thewireless communication terminal, the wireless communication terminalmaking a notification of the communication system when the wirelesscommunication base station permits connection of the wirelesscommunication terminal, the wireless communication base station conductsthe communication with the wireless communication terminal on the secondfrequency channel using the communication system when permitting arequest from the wireless communication terminal to change the firstfrequency channel to the second frequency channel, the communicationsystem being able to be used by the wireless communication terminal onthe connection management table from the identifier of the wirelesscommunication terminal in the communication systems used on the secondfrequency channel, the wireless communication terminal retains acommunication system in a connection management table along with anidentifier of a frequency channel, the communication system being usedon the second frequency channel, the wireless communication base stationnotifying the wireless communication terminal of the communicationsystem used on the second frequency channel, and the wirelesscommunication terminal conducts the communication with the wirelesscommunication base station on the second frequency channel using thecommunication system when the wireless communication base stationpermits the request of change to the second frequency channel, thecommunication system being used by the wireless communication basestation on the connection management table in the communication systemswhich can be used on the second frequency channel.

(Effect of Additional Statement (21))

The wireless communication base station notifies the wirelesscommunication terminal on the first frequency channel of thecommunication system used on the second frequency channel, so that thewireless communication terminal which performs the transmission andreception on the first frequency channel can recognize the communicationsystem which is used on the second frequency channel by the wirelesscommunication base station. Additionally, the wireless communicationterminal notifies the connected wireless communication base station onthe first frequency channel of the communication system which can beused on the second frequency channel, so that the wireless communicationbase station can previously recognize the communication system which canbe used on the second frequency channel of the wireless communicationterminal. Therefore, the wireless communication base station and thewireless communication terminal can previously recognize thecommunication system which should be used on the second frequencychannel, and the communication can be started without performing theexchange of the connection information again, the exchange of theconnection information being necessary for the communication in makingthe transition to the second frequency channel.

(21-1) In accordance with a forty-eighth aspect of the embodiments, awireless communication system includes a wireless communication basestation which can simultaneously conduct communication on at least twofrequency channels and a wireless communication terminal which cansimultaneously conduct communication on at least two frequency channelsand selecting at least one of the frequency channels to conduct thecommunication, and the wireless communication system is characterized inthat the wireless communication base station notifies the wirelesscommunication terminal of an identifier of a second frequency channeland a communication system on a first frequency channel, the secondfrequency channel being in a wireless packet receivable state except forthe first frequency channel, the communication system being used on thesecond frequency channel, the wireless communication terminal notifiesthe wireless communication base station of communication systems on thefirst frequency channel, the communication systems being able to be usedon the first frequency channel of the wireless communication terminal,the wireless communication terminal conducts the communication with thewireless communication base station on the first frequency channel whenthe wireless communication base station permits the connection, thewireless communication terminal notifies the wireless communication basestation of the communication system which can be used on the secondfrequency channel during the communication, the wireless communicationbase station retains the communication system in a connection managementtable along with an identifier of the wireless communication terminaland an identifier of a frequency channel, the communication system beingable to be used on the first frequency channel of the wirelesscommunication terminal, the wireless communication terminal making anotification of the communication system when the wireless communicationbase station permits connection of the wireless communication terminal,the wireless communication base station adds the identifier of thesecond frequency channel and information on the communication system tothe connection management table while correlating the identifier of thesecond frequency channel and the information with the identifier of thewireless communication terminal when the wireless communication terminalnotifies the wireless communication base station of the communicationsystem which can be used on the second frequency channel, thecommunication system being able to be used on the second frequencychannel of the wireless communication terminal, the wirelesscommunication base station conducts the communication with the wirelesscommunication terminal on the second frequency channel using thecommunication system when permitting a request from the wirelesscommunication terminal to change the first frequency channel to thesecond frequency channel, the communication system being able to be usedby the wireless communication terminal on the connection managementtable from the identifier of the wireless communication terminal in thecommunication systems used on the second frequency channel, the wirelesscommunication terminal retains a communication system in a connectionmanagement table along with an identifier of a frequency channel, thecommunication system being used on the second frequency channel, thewireless communication base station notifying the wireless communicationterminal of the communication system used on second frequency channel,and the wireless communication terminal conducts the communication withthe wireless communication base station on the second frequency channelusing the communication system when the wireless communication basestation permits the request of change to the second frequency channel,the communication system being used by the wireless communication basestation on the connection management table in the communication systemswhich can be used on the second frequency channel.

(Effect of Additional Statement (21-1))

The effects similar to those of the above-described aspect of theembodiments can be obtained, that is, after the connection isestablished on the first frequency channel, the wireless communicationterminal additionally notifies the wireless communication base stationof the communication system which can be used on the second frequencychannel by the wireless communication terminal. Therefore, a delay canbe granted in order to prepare a notification frame relating to thecommunication system which can be used on the second frequency channelof the wireless communication terminal, and the communication cancontinuously be conducted with no re-setting after the channel changewhile a load is reduced during a connection setting.

(21-2) In accordance with a forty-ninth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (21) or (21-1), and ischaracterized in that, when the usable communication system is changed,the wireless communication terminal notifies the wireless communicationbase station which permits the connection again of the usablecommunication system or of the usable frequency channel and the usablecommunication system, and the wireless communication base stationupdates the corresponding information in the connection management tablewhen receiving the renotification of the usable communication system orthe renotifications of the usable frequency channel and the usablecommunication system from the wireless communication terminal whoseconnection is permitted.

(Effect of Additional Statement (21-2))

The wireless communication base station is notified again of theinformation when the communication system which can be used by thewireless communication terminal is changed, so that the wirelesscommunication terminal and the wireless communication base station canconduct the communication with each other by the appropriatecommunication system which is supported with the communication state ofthe wireless communication terminal.

(21-3-1) In accordance with a fiftieth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (21), and is characterized in thatthe communication system is expressed by the type of the communicationstandard.

(Effect of Additional Statement (21-3-1))

The wireless communication base station notifies the wirelesscommunication terminal on the first frequency channel of the type of thecommunication standard which is used on the second frequency channel, sothat the wireless communication terminal which performs the transmissionand reception on the first frequency channel can recognize the type ofthe communication standard which is used on the second frequency channelby the wireless communication base station. Additionally, the wirelesscommunication terminal notifies the connected wireless communicationbase station on the first frequency channel of the type of thecommunication standard which can be used on the second frequencychannel, so that the wireless communication base station can previouslyrecognize the type of the communication standard which can be used onthe second frequency channel of the wireless communication terminal.Therefore, the wireless communication base station and the wirelesscommunication terminal can previously recognize the type of thecommunication standard which should be used on the second frequencychannel, and the communication can be started without making theexchange of the connection information again necessary for thecommunication in making the transition to the second frequency channel.

(21-3-2) In accordance with a fifty-first aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (21-3-1), and the wirelesscommunication system is characterized in that, in the type of thecommunication standard, extended systems in the same communicationstandard are distinguished from each other.

(Effect of Additional Statement (21-3-2))

The wireless communication base station notifies the wirelesscommunication terminal on the first frequency channel of the type of theextended systems in the same communication standard which is used on thesecond frequency channel, so that the wireless communication terminalwhich performs the transmission and reception on the first frequencychannel can recognize the type of the extended systems in the samecommunication standard which can be used on the second frequency channelof the wireless communication base station. Additionally, the wirelesscommunication terminal notifies the connected wireless communicationbase station on the first frequency channel of the type of the extendedsystems in the same communication standard which can be used on thesecond frequency channel, so that the wireless communication basestation can previously recognize the type of the extended systems in thesame communication standard which can be used on the second frequencychannel of the wireless communication terminal. Therefore, the wirelesscommunication base station and the wireless communication terminal canpreviously recognize the type of the extended systems in thecommunication standard which should be used on the second frequencychannel, and the communication can be started without making theexchange of the connection information again necessary for thecommunication in making the transition to the second frequency channel.

(22) In accordance with a fifty-second aspect of the embodiments, awireless communication system includes a wireless communication basestation which can simultaneously conduct communication on at least twofrequency channels using plural modulation and coding schemes, and awireless communication terminal which can simultaneously conductcommunication on at least two frequency channels using plural modulationand coding schemes, selecting at least one of the frequency channels toconduct the communication, and the wireless communication system ischaracterized in that the wireless communication base station notifiesthe wireless communication terminal of an identifier of a secondfrequency channel and a modulation and coding scheme on a firstfrequency channel, the second frequency channel being in a wirelesspacket receivable state except for the first frequency channel, themodulation and coding scheme being used on the second frequency channel,the wireless communication terminal notifies the wireless communicationbase station of at least a modulation and coding scheme on the firstfrequency channel in addition to the modulation and coding scheme whichcan be used on the first frequency channel of the wireless communicationterminal when transmitting the connection request to the wirelesscommunication base station on the first frequency channel, themodulation and coding scheme being able to be used by the wirelesscommunication terminal in the modulation and coding schemes on thesecond frequency channel, the wireless communication base stationnotifying the wireless communication terminal on the first frequencychannel of the modulation and coding schemes on the second frequencychannel, the wireless communication base station retains the modulationand coding scheme in a connection management table along with anidentifier of the wireless communication terminal and an identifier of afrequency channel, the modulation and coding scheme being able to beused by the wireless communication terminal, the wireless communicationterminal making a notification of the modulation and coding scheme whenthe wireless communication base station receives and permits aconnection request from the wireless communication terminal, thewireless communication base station determines whether or not themodulation and coding scheme can be used on the second frequency channelfrom the identifier of the wireless communication terminal whenreceiving a request from the wireless communication terminal to changethe first frequency channel to the second frequency channel, themodulation and coding scheme being able to be used by the wirelesscommunication terminal on a connection management table, the wirelesscommunication base station updates the identifier of the frequencychannel to the identifier of the second frequency channel and retainsthe identifier of the second frequency channel when determining thatmodulation and coding scheme can be used on the second frequencychannel, the wireless communication base station conducts thecommunication with the wireless communication terminal on the secondfrequency channel using the modulation and coding scheme which can beused by the wireless communication terminal on the connection managementtable from the identifier of the wireless communication terminal in themodulation and coding schemes used on the second frequency channel, thewireless communication terminal retains a modulation and coding schemein a connection management table along with an identifier of a frequencychannel, the modulation and coding scheme being used on the secondfrequency channel, the wireless communication base station notifying thewireless communication terminal of the modulation and coding scheme usedon the second frequency channel, the wireless communication terminalsends a request of change to the second frequency channel to thewireless communication base station, and the wireless communicationterminal conducts the communication with the wireless communication basestation on the second frequency channel using the modulation and codingscheme when the wireless communication base station permits the requestof the change to the second frequency channel, the modulation and codingscheme being used by the wireless communication base station on theconnection management table in the modulation and coding schemes whichcan be used on the second frequency channel.

(Effect of Additional Statement (22))

The wireless communication base station notifies the wirelesscommunication terminal on the first frequency channel of the modulationand coding scheme used on the second frequency channel, so that thewireless communication terminal which performs the transmission andreception on the first frequency channel can recognize the modulationand coding scheme which is used on the second frequency channel by thewireless communication base station. Additionally, the wirelesscommunication terminal notifies the connected wireless communicationbase station on the first frequency channel of the modulation and codingscheme which can be used on the second frequency channel, so that thewireless communication base station can previously recognize themodulation and coding scheme which can be used on the second frequencychannel of the wireless communication terminal. Therefore, the wirelesscommunication base station and the wireless communication terminal canpreviously recognize the modulation and coding scheme which should beused on the second frequency channel, and the communication can bestarted without performing the exchange of the connection informationagain, the exchange of the connection information being necessary forthe communication in making the transition to the second frequencychannel.

In the connection and in the channel change, the request is sent fromthe wireless communication terminal, and the response is received fromthe wireless communication base station. Therefore, consistency of theconnection information can be assured between the wireless communicationterminal and the wireless communication base station.

(22-1) In accordance with a fifty-second aspect of the embodiments, awireless communication system includes a wireless communication basestation which can simultaneously conduct communication on at least twofrequency channels using plural modulation and coding schemes, and awireless communication terminal which can simultaneously conductcommunication on at least two frequency channels using plural modulationand coding schemes, and selecting at least one of the frequency channelsto conduct the communication, and the wireless communication system ischaracterized in that the wireless communication base station notifiesthe wireless communication terminal on a first frequency channel of anidentifier of the first frequency channel, a modulation and codingscheme used on the first frequency channel, an identifier of a secondfrequency channel, and a modulation and coding scheme used on the secondfrequency channel, the second frequency channel being in a wirelesspacket receivable state except for the first frequency channel, thewireless communication terminal notifies the wireless communication basestation of the modulation and coding scheme which can be used on thefirst frequency channel of the wireless communication terminal whentransmitting the connection request to the wireless communication basestation on the first frequency channel, the wireless communication basestation retains the modulation and coding scheme in a connectionmanagement table along with an identifier of the wireless communicationterminal and an identifier of a frequency channel, the modulation andcoding scheme being able to be used on the first frequency channel bythe wireless communication terminal, the wireless communication terminalmaking a notification of the modulation and coding scheme when thewireless communication base station receives and permits a connectionrequest from the wireless communication terminal, the wirelesscommunication terminal retains a modulation and coding scheme in aconnection management table along with an identifier of a frequencychannel when the wireless communication base station permits theconnection of the wireless communication terminal, the wirelesscommunication base station notifying the wireless communication terminalof the modulation and coding scheme used on the first and secondfrequency channel, the wireless communication terminal conducts thecommunication with the wireless communication base station on the firstfrequency channel using the modulation and coding scheme on theconnection management table which is used by the wireless communicationbase station in the modulation and coding schemes which can be used onthe first frequency channel, the wireless communication terminalnotifies the wireless communication base station of at least themodulation and coding scheme which can be used by the wirelesscommunication terminal in the modulation and coding schemes on thesecond frequency channel, the wireless communication base stationnotifying the wireless communication terminal on the first frequencychannel of the modulation and coding schemes on the second frequencychannel, the wireless communication base station adds the identifier ofthe second frequency channel and information on the modulation andcoding scheme which can be used on the second frequency channel of thewireless communication terminal to the connection management table whilecorrelating the identifier of the second frequency channel and theinformation with the identifier of the wireless communication terminalwhen the wireless communication terminal notifies the wirelesscommunication base station of the modulation and coding scheme which canbe used on the second frequency channel, the wireless communication basestation determines whether or not the modulation and coding scheme canbe used on the second frequency channel from the identifier of thewireless communication terminal when receiving a request from thewireless communication terminal to change the first frequency channel tothe second frequency channel, the modulation and coding scheme beingable to be used by the wireless communication terminal on a connectionmanagement table, the wireless communication base station updates theidentifier of the frequency channel to the identifier of the secondfrequency channel and retains the identifier of the second frequencychannel when determining that the modulation and coding scheme can beused on the second frequency channel, the wireless communication basestation conducts the communication with the wireless communicationterminal on the second frequency channel using the modulation and codingscheme which can be used by the wireless communication terminal on theconnection management table from the identifier of the wirelesscommunication terminal in the modulation and coding schemes used on thesecond frequency channel, the wireless communication terminal sends arequest of change to the second frequency channel to the wirelesscommunication base station, and the wireless communication terminalconducts the communication with the wireless communication base stationon the second frequency channel using the modulation and coding schemewhen the wireless communication base station permits the request of thechange to the second frequency channel, the modulation and coding schemebeing used by the wireless communication base station on the connectionmanagement table in the modulation and coding schemes which can be usedon the second frequency channel.

(Effect of Additional Statement (22-1))

The effects similar to those of the above-described aspect of theembodiments can be obtained, that is, after the connection isestablished on the first frequency channel, the wireless communicationterminal additionally notifies the wireless communication base stationof the modulation and coding scheme which can be used on the secondfrequency channel by the wireless communication terminal. Therefore, adelay can be granted in order to prepare a notification frame relatingto the modulation and coding scheme which can be used on the secondfrequency channel of the wireless communication terminal, and thecommunication can continuously be conducted with no re-setting after thechannel change while a load is reduced during a connection setting.

(22-2) In accordance with a fifty-third aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (22) or (22-1), and the wirelesscommunication system is characterized in that, when the usablemodulation and coding scheme is changed, the wireless communicationterminal notifies the wireless communication base station which permitsthe connection again of the usable modulation and coding scheme or ofthe usable frequency channel and the usable modulation and codingscheme, and the wireless communication base station updates thecorresponding information in the connection management table whenreceiving the renotification of the usable modulation and coding schemeor the renotifications of the usable frequency channel and the usablemodulation and coding scheme from the wireless communication terminalwhose connection is permitted.

(Effect of Additional Statement (22-2))

The wireless communication base station is notified again of theinformation when the modulation and coding scheme which can be used bythe wireless communication terminal is changed, so that the wirelesscommunication terminal and the wireless communication base station canconduct the communication with each other by the appropriate modulationand coding scheme which is supported with the communication state of thewireless communication terminal.

(23-1) In accordance with a fifty-fourth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (21), (21-1), (22), or (22-1), andis characterized in that the wireless communication base stationnotifies the wireless communication terminal on the second frequencychannel of the communication system or modulation and coding scheme usedon the second frequency channel.

(Effect of Additional Statement (23-1))

The notification of the communication system or modulation and codingscheme used on the second frequency channel is made on the secondfrequency channel, so that other wireless communication base stations orwireless communication terminals which are receivable on the secondfrequency channel can recognize what communication system or modulationand coding scheme is used on the second frequency channel by thewireless communication base station. In other wireless communicationbase stations or wireless communication terminals, aninterference-prevention measure can be taken by the recognition. In thewireless communication terminal, the wireless communication base stationcan be specified as a candidate of a connected wireless communicationbase station by such recognition.

(23-2) In accordance with a fifty-fifth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (21), (21-1), (22), or (22-1), andis characterized in that the wireless communication base stationnotifies the wireless communication terminal on the second frequencychannel that the wireless communication base station has the same firstfrequency channel.

(Effect of Additional Statement (23-2))

The notification of the identifier of the wireless communication basestation is made on the second frequency channel, so that thenotification that the same wireless communication base station isoperated on the first and second frequency channels is made on thesecond frequency channel. In other wireless communication base stationsor wireless communication terminals, an interference-prevention measurecan be taken by such recognition. The wireless communication terminalcan recognize the wireless communication base station to send thewireless packet. Additionally, the wireless communication terminalconducts the communication with the wireless communication base stationon the first frequency channel, changes the first frequency channel tothe second frequency channel, and conducts the communication again withthe wireless communication base station.

(23-2-1-1) In accordance with a fifty-sixth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (23-2), and is characterized inthat the wireless communication base station sends a wireless packet onall wireless packet sendable and receivable frequency channels, thewireless packet being addressed to all or a part of plural wirelesscommunication terminals, the wireless communication terminals beingconnected on one of frequency channels in wireless packet sendable andreceivable states.

(Effect of Additional Statement (23-2-1-1))

The wireless packet addressed to the plural wireless communicationterminals is sent on all the wireless packet sendable and receivablefrequency channels, so that the destination wireless communicationterminal that can move the frequency channel can securely receive thewireless packet. Additionally, it is not necessary that the wirelesscommunication base station correctly specify the connected frequencychannel including the movement of the frequency channel to connectwireless communication terminal in transmitting the wireless packet, sothat the load on processing can be reduced.

(23-2-1-2) In accordance with a fifty-seventh aspect of the embodiments,a wireless communication system is the wireless communication systemdescribed in the additional statement (23-2-1-1), and is characterizedin that the wireless communication base station inserts an identicalvalue in a item indicating the order of a delivery number whentransmitting the wireless packet addressed to all or a part of pluralwireless communication terminals on all the wireless packet sendable andreceivable frequency channels.

(Effect of Additional Statement (23-2-1-2))

The identical value is inserted in the item indicating the order of thedelivery number when the wireless packet addressed to the same pluralwireless communication terminals is sent on the plural frequencychannels. Therefore, when the transmission timing is shifted between theplural frequency channels, the wireless communication terminal which ismoved between the frequency channels during the shift of thetransmission timing or the wireless communication terminal which isreceivable on the plural frequency channels can recognize that thereceived packets are overlapping even if the wireless communicationterminal receives the same packets on the plural frequency channels.

(23-2-2-1) In accordance with a fifty-eighth aspect of the embodiments,a wireless communication system is the wireless communication systemdescribed in the additional statement (23-2), and is characterized inthat, in the wireless communication base station, a first item and asecond item are provided in the wireless packet used in thenotification, the first item indicating the identifier of the wirelesscommunication base station which is also used in the wirelesscommunication base station which can conduct communication only on thesingle frequency channel, the identifier inserted in the first itemdiffers from channel to channel, and the identifier indicating the samewireless communication base station between the frequency channels isinserted in the second field.

(Effect of Additional Statement (23-2-2-1))

The notification of the same wireless communication base station as thefirst frequency channel is made by the item different from the itemindicating the identifier of the wireless communication base stationwhich is used in the wireless communication base station which canconduct the communication only on the single frequency channel.Therefore, when the notification is received by the wirelesscommunication terminal which can be connected only to the wirelesscommunication base station which can conduct the communication only onthe single frequency channel, the wireless communication base stationwhich can conduct the communication only on the single frequency channelcan be recognized as another wireless communication base station toconnect the wireless communication terminal to the wirelesscommunication base station. In the wireless communication terminal whichcan be connected to the wireless communication base station which canconduct the communication on the plural frequency channels, the wirelesscommunication terminal can recognize the wireless communication basestation which can conduct the communication on the plural frequencychannels as the same wireless communication base station to connect thewireless communication terminal to the wireless communication basestation.

(25) In accordance with a fifty-ninth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (21), (21-1), (22), or (22-1), andis characterized in that the identifier of the wireless communicationterminal in the connection management table retained by the wirelesscommunication base station is a management number allocated to thewireless communication terminal when the wireless communication basestation permits the wireless communication terminal to be connectedthereto.

(Effect of Additional Statement (25))

The management number allocated to the wireless communication terminalwhen the wireless communication base station permits the wirelesscommunication terminal to be connected thereto is retained as theidentifier of the wireless communication terminal by the connectionmanagement table, so that the wireless communication base station canidentify the wireless communication terminal using the uniqueidentifier, and the management of the wireless communication terminalcan be simplified.

(26) In accordance with a sixtieth aspect of the embodiments, a wirelesscommunication system is the wireless communication system described inthe additional statement (21), (21-1), (22), or (22-1), and ischaracterized in that the wireless communication base station includes aqueue in which the sent wireless packet is stored in each frequencychannel, and the wireless packet addressed to the wireless communicationterminal is moved from a first queue for the first frequency channel toa second queue for the second frequency channel when the wirelesscommunication base station permits the request from the wirelesscommunication terminal to change the first frequency channel to thesecond frequency channel is permitted.

(Effect of Additional Statement (26))

The wireless communication base station includes the queue in which thesent wireless packet is stored in each frequency channel, and thewireless packet addressed to the wireless communication terminal ismoved to the transmission queue of the supported frequency channel inresponse to the frequency channel change request from the wirelesscommunication terminal. Therefore, the wireless communication terminalmoved between the frequency channels can send the wireless packetaddressed to the wireless communication terminal on the appropriatefrequency channel on which the communication is conducted.

(27) In accordance with a sixty-first aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (21), (21-1), (22), or (22-1), andis characterized in that, when the wireless communication base stationpermits the request from the wireless communication terminal to changethe first frequency channel to the second frequency channel, thewireless communication base station starts the communication with thewireless communication terminal on the second frequency channel after atleast a fixed time elapses since the permission.

(Effect of Additional Statement (27))

The wireless communication base station starts the communication withthe wireless communication terminal on the changed frequency channelafter at least the fixed time elapses since the request from thewireless communication terminal to change the first frequency channel tothe second frequency channel is permitted. Therefore, a delay can begranted in order to prepare the start of the communication between thewireless communication base station and the wireless communicationterminal on the changed frequency channel.

(27-1) In accordance with a sixty-second aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (27), and is characterized in thatat least a time necessary to move the frequency channel of the wirelesscommunication terminal is set at the fixed time.

(Effect of Additional Statement (27-1))

The communication is started between the wireless communication basestation and the wireless communication terminal on the changed frequencychannel after at least the time necessary to move the frequency channelof the wireless communication terminal elapses. Therefore, that thewireless communication terminal is in the receivable state on thechanged frequency channel can be assured to start the transmission ofthe wireless packet.

(27-1-1) In accordance with a sixty-third aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (27-1), and is characterized inthat the wireless communication base station obtains a time necessary tochange the frequency channel from the wireless communication terminalbefore permitting the request to change the first frequency channel tothe second frequency channel of the wireless communication terminal.

(Effect of Additional Statement (27-1-1))

The time necessary to change the frequency channel is obtained from thewireless communication terminal before the request to change the firstfrequency channel to the second frequency channel is permitted, and thetime necessary to move the frequency channel of the wirelesscommunication terminal is correctly recognized. Then the communicationis started between the wireless communication base station and thewireless communication terminal on the changed frequency channel afterat least the time elapses, so that a degree of certainty can be enhancedfor the assurance that the wireless communication terminal is in thereceivable state on the changed frequency channel.

(27-2) In accordance with a sixty-fourth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (26), and is characterized inthat, when the wireless communication base station permits the requestfrom the wireless communication terminal to change the first frequencychannel to the second frequency channel, the wireless communication basestation starts the communication with the wireless communicationterminal on the second frequency channel after at least the timenecessary to move the wireless packet from the first queue to the secondqueue in the wireless communication base station elapses since thepermission.

(Effect of Additional Statement (27-2))

The wireless communication base station starts the communication withthe wireless communication terminal on the changed frequency channelafter at least the time necessary to move the wireless packet addressedto the wireless communication terminal between the queues in thewireless communication base station elapses, so that the wireless packetaddressed to the wireless communication terminal can surely be sent tothe wireless communication terminal on the changed frequency channel.

(27-3) In accordance with a sixty-fifth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (27), and is characterized in thata determination of the fixed time is made by exchange of the wirelesspacket between the wireless communication base station and the wirelesscommunication terminal before the change to the second frequency channelis permitted.

(Effect of Additional Statement (27-3))

The time to start the communication with the wireless communicationterminal on the changed frequency channel is determined by the exchangeof the wireless packet, so that the start of the communication can beassured after the communication can surely be conducted between thewireless communication base station and the wireless communicationterminal on the changed frequency channel.

(28) In accordance with a sixty-sixth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (21), (21-1), (22), or (22-1), andis characterized in that the wireless communication base stationnotifies the wireless communication terminal on the first frequencychannel of a usage rate of the second frequency channel, and thewireless communication terminal determines whether or not the wirelesscommunication terminal sends the request to transfer to the secondfrequency channel based on the usage rate of the second frequencychannel from the wireless communication base station.

(Effect of Additional Statement (28))

The wireless communication base station notifies the wirelesscommunication terminal of the usage rate of another frequency channel.Therefore, the wireless communication base station can provide theinformation as to whether or not the wireless communication terminalmakes the transition to another frequency channel, and the wirelesscommunication terminal can make the determination of the transition toanother frequency channel based on the information to assure thecommunication on the transferred frequency channel.

(29) In accordance with a sixty-seventh aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (21), (21-1), (22), or (22-1), andis characterized in that the wireless communication base stationnotifies the wireless communication terminal on the first frequencychannel of a second bandwidth which is the bandwidth of the secondfrequency channel, and the wireless communication terminal determineswhether or not the wireless communication terminal sends the request totransfer to the second frequency channel based on the second bandwidthfrom the wireless communication base station.

(Effect of Additional Statement (29))

The wireless communication base station notifies the wirelesscommunication terminal of the bandwidth of another frequency channel, sothat the wireless communication terminal can make the determination ofwhether or not another frequency channel has a bandwidth in which thewireless communication terminal can conduct communication, and assurethe communication on the transferred frequency channel.

(30) In accordance with a sixty-eighth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (21), (21-1), (22) or (22-1), andis characterized in that the wireless communication base station retainssecurity information in the connection management table whilecorrelating the security information with the identifier of the wirelesscommunication terminal, the security information being set in conductingthe communication with the wireless communication terminal on the firstfrequency channel, and the communication is conducted with the wirelesscommunication terminal on the second frequency channel using theretained security information when the request from the wirelesscommunication terminal to change the first frequency channel to thesecond frequency channel is permitted.

(Effect of Additional Statement (30))

The wireless communication base station manages the security informationalong with the identifier of the wireless communication terminal, andthe same security information is used on the changed frequency channelwhen the request of the change to another frequency channel ispermitted, so that the communication can be started between the wirelesscommunication base station and the wireless communication terminalunless the security setting is performed again on the changed frequencychannel.

(30-1) In accordance with a sixty-ninth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (30), and is characterized in thatthe wireless communication terminal notifies the wireless communicationbase station on the first frequency channel of the security system whichcan be used on the first and second frequency channels, the wirelesscommunication base station retains a security system which can be usedby the wireless communication terminal in the connection managementtable while correlating the security system with the identifier of thewireless communication terminal, the wireless communication terminalnotifying the wireless communication base station of the securitysystem, the wireless communication base station refers to whether or notthe security system is matched with a security system necessary for thewireless communication base station on the second frequency channel fromthe connection management table when the wireless communication terminalmakes the request to change the first frequency channel to the secondfrequency channel, and the reference is used to make the determinationof the permission.

(Effect of Additional Statement (30-1))

The wireless communication base station recognizes the security systemwhich can be used by the wireless communication terminal before therequest of the change to another frequency channel, and uses thesecurity system for determining whether or not the wirelesscommunication base station permits the request of the change to anotherfrequency channel, so that the security can be retained on anotherfrequency channel. Additionally, when the security system necessary forthe wireless communication base station is not satisfied, the wirelesscommunication terminal previously recognizes the connection request fromthe wireless communication terminal which is known to be rejected onanother frequency channel, so that the occupancy of the frequencychannel caused by the exchange of the wireless packet due to the wastedconnection can be reduced. When the wireless communication base stationpermits the wireless communication terminal to be changed to anotherfrequency channel, the information on the security system of which thewireless communication terminal notifies the wireless communication basestation can be used in the communication with the wireless communicationterminal on the changed frequency channel.

(30-1-1) In accordance with a seventieth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (30-1), and is characterized inthat, when the wireless communication base station permits the requestfrom the wireless communication terminal of the change to the secondfrequency channel, the communication is conducted with the wirelesscommunication terminal on the second frequency channel using informationon the retained security setting when a first security system used onthe first frequency channel can be used on the second frequency channel,one of the corresponding security systems which are supported with thesecond frequency channel of the wireless communication base station inthe security systems which can be used on the second frequency channelby the wireless communication terminal is selected as a second securitysystem from the connection management table when the first securitysystem cannot be used on the second frequency channel, and the secondsecurity system is set before the communication is conducted with thewireless communication terminal using the security system on the secondfrequency channel.

(Effect of Additional Statement (30-1-1))

When the security system before the frequency channel change can be usedas the frequency channel after the frequency channel change, thecommunication is conducted using the same security information, so thatthe re-setting of the exchange of the wireless packet can be omitted.The exchange of the wireless packet is re-set in order to use thesecurity system on the changed frequency channel. When the securitysystems supported with the wireless communication terminal exist in thesecurity systems necessary for the wireless communication base stationalthough the security system before the frequency channel change cannotbe used on the changed frequency channel, the setting of one of thesecurity systems which are supported with the wireless communicationterminal is performed on the changed frequency channel between thewireless communication base station and the wireless communicationterminal, so that the security necessary for the wireless communicationbase station on the changed frequency channel can be retained.

(30-2) In accordance with a seventieth aspect of the embodiments, awireless communication system is the wireless communication systemdescribed in the additional statement (30-1), and is characterized inthat the wireless communication base station notifies the wirelesscommunication terminal on the first frequency channel of the securitysystem necessary for the second frequency channel.

(Effect of Additional Statement (30-2))

The wireless communication base station notifies the wirelesscommunication terminal of the security level necessary for anotherfrequency channel. Therefore, a security level necessary for anotherfrequency channel can be changed, and the wireless communicationterminal can determine whether or not another frequency channel issupported with the security system of the wireless communicationterminal.

(31-0-1) The wireless communication base station described in theadditional statement (1) or (1-1), the wireless communication terminaldescribed in the additional statement (11) or (11-1), or the wirelesscommunication system described in the additional statement (21) or(21-1) is characterized in that the communication system which can beused by the wireless communication terminal is a communication systemwhich can be received at least by the wireless communication terminal.

(Effect of Additional Statement (31-0-1))

The wireless communication terminal notifies the wireless communicationbase station of the communication system which can be received by thewireless communication terminal. Therefore, a selection range of thecommunication system addressed to the wireless communication terminalfrom the wireless communication base station can be widened, when thereceivable communication system differs from the sendable communicationsystem, particularly when the range of the receivable communicationsystem is wider than that of the sendable communication system.

(31-0-2) The wireless communication base station described in theadditional statement (1) or (1-1), the wireless communication terminaldescribed in the additional statement (11) or (11-1), or the wirelesscommunication system described in the additional statement (21) or(21-1) is characterized in that the communication system which can beused by the wireless communication terminal is a communication systemwhich can be received and sent at least by the wireless communicationterminal.

(Effect of Additional Statement (31-0-2))

The wireless communication base station is notified of the communicationsystem which can be received and sent by the wireless communicationterminal, so that the wireless communication base station can performthe transmission by the communication system which can be received bythe wireless communication terminal. The wireless communication basestation recognizes the communication system which can be sent from thewireless communication terminal, so that the communication system whichcan be sent from the wireless communication terminal can be used asinformation in performing adaptive control. The type of thecommunication system of the wireless packet sent from the wirelesscommunication terminal is narrowed, so that the wireless communicationbase station can easily correspond to the reception system.

(31-0-3) The wireless communication base station described in theadditional statement (1) or (1-1), the wireless communication terminaldescribed in the additional statement (11) or (11-1), or the wirelesscommunication system described in the additional statement (21) or(21-1) is characterized in that the communication system which can beused by the wireless communication terminal is a communication system inwhich communication system that can be received by the wirelesscommunication terminal and a communication system that can be sent bythe wireless communication terminal are distinguished from each other.

(Effect of Additional Statement (31-0-3))

The wireless communication terminal notifies the wireless communicationbase station of the communication system which can be received by thewireless communication terminal. Therefore, a selection range of thecommunication system addressed to the wireless communication terminalfrom the wireless communication base station can be widened, when thereceivable communication system differs from the sendable communicationsystem, particularly when the range of the receivable communicationsystem is wider than that of the sendable communication system.

The wireless communication base station is notified of the communicationsystem which can be sent by the wireless communication terminal, so thatthe wireless communication base station can use the communication systemwhich can be sent from the wireless communication terminal asinformation in performing adaptive control of the communication betweenthe wireless communication base station and the wireless communicationterminal. The type of the communication system of the wireless packetsent from the wireless communication terminal is narrowed, so that thewireless communication base station can easily correspond to thereception system.

(31-1-1) The wireless communication base station described in theadditional statement (1) or (1-1), the wireless communication terminaldescribed in the additional statement (11) or (11-1), or the wirelesscommunication system described in the additional statement (21) or(21-1) is characterized in that the modulation and coding scheme whichcan be used by the wireless communication terminal is a modulation andcoding scheme which can be received at least by the wirelesscommunication terminal.

(Effect of Additional Statement (31-1-1))

The wireless communication terminal notifies the wireless communicationbase station of the modulation and coding scheme which can be receivedby the wireless communication terminal. Therefore, a selection range ofthe modulation and coding scheme addressed to the wireless communicationterminal from the wireless communication base station can be widened,when the receivable modulation and coding scheme differs from thesendable modulation and coding scheme, particularly when the range ofthe receivable modulation and coding scheme is wider than that of thesendable modulation and coding scheme.

(31-1-2) The wireless communication base station described in theadditional statement (1) or (1-1), the wireless communication terminaldescribed in the additional statement (11) or (11-1), or the wirelesscommunication system described in the additional statement (21) or(21-1) is characterized in that the modulation and coding scheme whichcan be used by the wireless communication terminal is a modulation andcoding scheme which can be received and sent by the wirelesscommunication terminal.

(Effect of Additional Statement (31-1-2))

The wireless communication base station is notified of the modulationand coding scheme which can be received and sent by the wirelesscommunication terminal, so that the wireless communication base stationcan perform the transmission by the modulation and coding scheme whichcan be received by the wireless communication terminal. The wirelesscommunication base station recognizes the modulation and coding schemewhich can be sent from the wireless communication terminal, so that themodulation and coding scheme which can be sent from the wirelesscommunication terminal can be used as information in performing adaptivecontrol. The type of the modulation and coding scheme of the wirelesspacket sent from the wireless communication terminal is narrowed, sothat the wireless communication base station can easily correspond tothe reception system.

(31-1-3) The wireless communication base station described in theadditional statement (1) or (1-1), the wireless communication terminaldescribed in the additional statement (11) or (11-1), or the wirelesscommunication system described in the additional statement (21) or(21-1) is characterized in that the modulation and coding scheme whichcan be used by the wireless communication terminal is a modulation andcoding scheme in which a modulation and coding scheme that can bereceived by the wireless communication terminal and a modulation andcoding scheme that can be sent by the wireless communication terminalare distinguished from each other.

(Effect of Additional Statement (31-1-3))

The wireless communication terminal notifies the wireless communicationbase station of the modulation and coding scheme which can be receivedby the wireless communication terminal. Therefore, a selection range ofthe modulation and coding scheme addressed to the wireless communicationterminal from the wireless communication base station can be widened,when the receivable modulation and coding scheme differs from thesendable modulation and coding scheme, particularly when the range ofthe receivable modulation and coding scheme is wider than that of thesendable modulation and coding scheme.

The wireless communication base station is notified of the modulationand coding scheme which can be sent by the wireless communicationterminal, so that the wireless communication base station can use themodulation and coding scheme which can be sent from the wirelesscommunication terminal as information in performing adaptive control ofthe communication between the wireless communication base station andthe wireless communication terminal. The type of the modulation andcoding scheme of the wireless packet sent from the wirelesscommunication terminal is narrowed, so that the wireless communicationbase station can easily correspond to the reception system.

(32-1) The wireless communication base station described in theadditional statement (8), the wireless communication terminal describedin the additional statement (17), or the wireless communication systemdescribed in the additional statement (28) is characterized in that theusage rate of the second frequency channel is an average amount of datawhich the wireless communication base station sends per unit time on thesecond frequency channel.

(Effect of Additional Statement (32-1))

The wireless communication base station provides the average amount ofdata which is sent per unit time on another frequency channel, so thatthe wireless communication base station can provide the information tothe wireless communication terminal in order to make the determinationof the transition to another frequency channel.

(32-2) The wireless communication base station described in theadditional statement (8), the wireless communication terminal describedin the additional statement (17), or the wireless communication systemdescribed in the additional statement (28) is characterized in that theusage rate of the second frequency channel is a channel occupancy rateof the wireless communication base station on the second frequencychannel.

(Effect of Additional Statement (32-2))

The wireless communication base station provides the channel occupancyrate on another frequency channel, so that the wireless communicationbase station can provide the information to the wireless communicationterminal in order to make the determination of the transition to anotherfrequency channel.

(32-3) The wireless communication base station described in theadditional statement (8), the wireless communication terminal describedin the additional statement (17), or the wireless communication systemdescribed in the additional statement (28) is characterized in that theusage rate of the second frequency channel is an average time to obtainan access right since the access request is made when the wirelesscommunication base station sends the wireless packet on the secondfrequency channel.

(Effect of Additional Statement (32-3))

The wireless communication base station provides the average time toobtain the access right on another frequency channel, so that thewireless communication base station can provide the information to thewireless communication terminal in order to make the determination ofthe transition to another frequency channel.

(33-1) The wireless communication base station described in theadditional statement (9), the wireless communication terminal describedin the additional statement (18), or the wireless communication systemdescribed in the additional statement (29) is characterized in that thesecond bandwidth is at least two and an integral multiple of the firstbandwidth which is the bandwidth of the first frequency channel.

(Effect of Additional Statement (33-1))

The wireless communication base station provides the information thatthe bandwidth of another frequency channel is at least two and theintegral multiple of the first bandwidth to the wireless communicationterminal. Therefore, the wireless communication terminal can easilydetermine whether or not another frequency channel has the bandwidth inwhich the wireless communication terminal can conduct the communication,and the bandwidth extended communication system can easily be realized.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A wireless communication apparatus capable ofcommunicating via a first frequency bandwidth and a second frequencybandwidth, comprising: a transmitter to transmit, via the firstfrequency bandwidth, a first frame including information relating to thesecond frequency bandwidth, a center frequency of the second frequencybandwidth and a group identifier for communication via the secondfrequency bandwidth; and a receiver to receive, via the first frequencybandwidth, a second frame for changing to the second frequencybandwidth, wherein the transmitter transmits, via the second frequencybandwidth, a third frame after the receiver receives the second frame.2. The apparatus according to claim 1, wherein the group identifier isused for communication via the first frequency bandwidth and the secondfrequency bandwidth.
 3. The apparatus according to claim 1, wherein thereceiver receives an association request frame which includescapabilities information for communication via at least one of the firstfrequency bandwidth and the second frequency bandwidth, and thetransmitter transmits the third frame using the capabilities informationfor communication via the second frequency bandwidth.
 4. The apparatusaccording to claim 1, wherein the capabilities information includes aplurality of modulation and coding schemes.
 5. The apparatus accordingto claim 3, further comprising a memory to store a connection managementtable having the capabilities information, wherein the transmitterrefers to the connection management table in connection with sending thethird frame.
 6. The apparatus according to claim 1, wherein the firstfrequency bandwidth and the second frequency bandwidth include frequencyranges that partly overlap with each other.
 7. The apparatus accordingto claim 1, wherein the group identifier is a BSSID, the first frame isa beacon frame, the second frame is a management frame and the thirdframe is a data frame.
 8. The apparatus according to claim 1, furthercomprising an antenna to transmit a radio wave of the first frame. 9.The apparatus according to claim 1, wherein the transmitter and thereceiver include baseband circuitry and frequency conversion circuitry.10. The apparatus according to claim 1, further comprising: a firstqueue for the first frequency bandwidth; and a second queue for thesecond frequency bandwidth, wherein the transmitter shifts the thirdframe stored in the first queue to the second queue after the receiverreceives the second frame.
 11. A wireless communication apparatuscapable of communicating via a first frequency bandwidth and a secondfrequency bandwidth, comprising: a receiver to receive, via the firstbandwidth, a first frame including information relating to the secondfrequency bandwidth, a center frequency of the second frequencybandwidth and a group identifier for communication via the secondfrequency bandwidth; and a transmitter to transmit, via the firstfrequency bandwidth, a second frame to change to the second frequencybandwidth, wherein the transmitter transmits, via the second frequencybandwidth, a third frame after transmitting the second frame.
 12. Theapparatus according to claim 11, wherein the group identifier is usedfor communication via the first frequency bandwidth and the secondfrequency bandwidth.
 13. The apparatus according to claim 11, whereinthe transmitter transmits an association request frame which includesinformation relating to capabilities information for communication viaat least one of the first frequency bandwidth and the second frequencybandwidth.
 14. The apparatus according to claim 11, wherein the groupidentifier is a BSSID, the first frame is a beacon frame, the secondframe is a management frame and the third frame is a data frame.
 15. Theapparatus according to claim 11, further comprising an antenna totransmit a radio wave of the second frame.
 16. The apparatus accordingto claim 11, wherein the transmitter and the receiver include basebandcircuitry and frequency conversion circuitry.
 17. The apparatusaccording to claim 11, further comprising: a first queue for the firstfrequency bandwidth; and a second queue for the second frequencybandwidth, wherein the transmitter shifts the third frame stored in thefirst queue to the second queue after transmitting the second frame. 18.The apparatus according to claim 11, wherein the transmitter transmitsthe second frame when a channel usage rate of the second frequencybandwidth is lower than a channel usage rate of the first frequencybandwidth.
 19. A wireless communication method for communicating via afirst frequency bandwidth and a second frequency bandwidth, comprising:sending, via the first frequency bandwidth, a first frame includinginformation relating to the second frequency bandwidth, a centerfrequency of the second frequency bandwidth and a group identifier forcommunication via the second frequency bandwidth; receiving, via thefirst frequency bandwidth, a second frame to change to the secondfrequency bandwidth; and sending, via the second frequency bandwidth, athird frame after receiving the second frame.
 20. The method accordingto claim 19, wherein the group identifier is used for communication viathe first frequency bandwidth and the second frequency bandwidth. 21.The method according to claim 19, wherein the group identifier is aBSSID and the first frame is a beacon frame.
 22. A wirelesscommunication method for communicating via a first frequency bandwidthand a second frequency bandwidth, comprising: receiving, via the firstfrequency bandwidth, a first frame including information relating to thesecond frequency bandwidth, a center frequency of the second frequencybandwidth and a group identifier for communication via the secondfrequency bandwidth; sending, via the first frequency bandwidth, asecond frame to change to the second frequency bandwidth; and sending,via the second frequency bandwidth, a third frame after sending thesecond frame.
 23. The method according to claim 22, wherein the groupidentifier is used for communication via the first frequency bandwidthand the second frequency bandwidth.
 24. The method according to claim22, wherein the group identifier is a BSSID and the first frame is abeacon frame.